ERTAS: The Engine of Consciousness

Part Of: Demystifying Consciousness sequence
Content Summary: 800 words, 8 min read

Existential Mode Generators

In Why We Sleep, we discussed sleep architecture diagrams. These diagrams show clear electrical differences between three existential modes: NREM (“sleeping”), REM (“dreaming”), and Consciousness.


While EEG excels at providing temporal resolution, it doesn’t provide much spatial information. Where does the brain construct these three modes?

To answer this, neuroscientists cut the brains of cats in half… literally. If you perform a Cerveau Isolé cut (slice above the midbrain), the top half’s electrical signature is NREM. If you do a Midpontine Pre-Trigeminal cut (slice below the midbrain), the top half’s electrical signature is NREM + Consciousness.

Consciousness Ignition- Localizing Circuits (2)

This evidence shows that existential modes are generated by different areas. Specifically:

  • Sleep is induced by the diencephalon.
  • Dreaming is initiated by the metencephalon.
  • Consciousness is ignited by the mesencephon.

Neuroscientists now knew where to look! It was not long before they discovered the machinery that create consciousness, sleeping, and dreaming:

Consciousness Ignition- Mode Localization (2)

We now turn our gaze to the ascending reticular activating system (ARAS).  “Reticular” is a word that means “web-like”, so the name roughly means “web-like ignition switch”.  But before we do so, we need to turn our gaze to the relationship between cortico-thalamic (CT) radiations and consciousness.

Thalamus Anatomy & Function

We have also explained that the purpose of consciousness is to solve the binding problem: gluing together disparate adjectives into coherent nouns:

Objects- Distributed Object Networks (2)

Consciousness creates the coherent objects of working memory by implementing phase binding, where object features are stitched together in distinct frequency bands, not unlike the radio in your car.

Objects- Phase Locking & Wakefulness

We have previously described the thalamus and cortex as dually innervating spheres, not dissimilar to a plasma globe:

Brain- Plasma Globe analogy (2)

And indeed, the nuclei within the thalamus tile the entire cortex:

Consciousness Ignition- Thalamic Architecture

Note, however, that only some thalamic nuclei are specific (project to discrete patches of cortex). Nonspecific thalamic nuclei are also present, including the Intralaminar Nuclei (ILN) and Reticular Nucleus of the Thalamus (RNT).

These nonspecific nuclei are the principal components of the ERTAS system, and plausible candidates for the engine of consciousness.

Damage of specific nuclei produce loss of a particular modality.  In contrast, lesions to nonspecific nuclei produces deep disturbances of consciousness. In fact, recent evidence suggests that such lesions perturb cortico-cortical information transmission.

The ERTAS Hypothesis

The ascending reticular activating system (ARAS) consists of a dense web of nuclei. Indeed, the word “reticular” means “web-like”. Parvizi, Damasio (2001) outline the more significant members of the system:

Consciousness Ignition- Mesencephalon Reticular Formation

These nuclei project to the following three sites:

  1. Reticular Nucleus of the Thalamus (RNT), a sheet that sits on top of the thalamus.
  2. Intralaminar Nuclei (ILN), which are embedded deep within the thalamus.
  3. Basal Forebrain, which receives & distributes several neurochemical systems.

These structures in turn route information flowing to cortex:

Consciousness Ignition- Thalamus ILC NR

The extended reticular-thalamic activating system (ERTAS) hypothesis connects the ARAS system with the phase binding interpretation of the cortico-thalamo-cortical reentrant loop. One hypothesis, adapted from Newman (1999), has three theses:

  • ILN performs phase binding (and thus, the consciousness generator).
  • RNT implements selective attention.
  • Basal Forebrain provides visceral “body-relevant” information.


More recent research has corroborated the role of the ILN in phase binding, and expanded its scope. Saalmann (2014) notes that the ILN seems to participate in a larger group of higher-order nuclei which each manage information within more constrained parts of cortex. The anterior ILN seems more related to oculomotor processes; the posterior deals with the multimodal integration of different sense data.

One unexpected recent finding has been that lesions of “higher-order nuclei” such as the ILN seem to perturb cortico-cortical information transmission. This underscores the need to understand interactions between the CTC Loop and other reentrant loops.


The Role of The Claustrum

The claustrum is a tiny sheet of gray matter suspended between thalamus and cortex. However, it receives information from essentially the entire cortex:

Consciousness Ignition- Claustrum Anatomy (2)

Given that the purpose of consciousness is to integrate cortical information, the anatomical position of the claustrum is suggestive.

Recent anatomical evidence has only strengthened the case for claustrum promoting consciousness:

  • Koubeissi et al  (2014) is a case study where they were electrical stimulation of the claustrum induced loss of consciousness (!).
  • Chau et al (2015) announced evidence that correlate claustrum lesions with the duration, but not the frequency, of loss of consciousness.
  • Wang et al (2016) conclusively proved that the claustrum has reciprocal connections everywhere in cortex.
  • Reardon (2017) announced the discovery of a single neuron whose dendrites encircled the entire brain (image credit)

Consciousness Ignition- Claustrum Mega-Neurons

These data are suggestive. However, it will be some time before we know enough to integrate claustrum function within the ERTAS system.

Until next time.

Related Works

  • Chau et al (2015). The effect of claustrum lesions on human consciousness and the recovery of function
  • Crick, Koch (2005). What is the function of the claustrum?
  • Koubeissi et al (2014). Electrical stimulation of a small brain area reversibly disrupts consciousness
  • Newman (1999). Putting the puzzle together: towards a general theory of the neural correlates of consciousness
  • Parvizi, Damasio (2001). Consciousness and the brainstem
  • Reardon (2017). A giant neuron found wrapped around entire mouse brain.
  • Wang et al (2016). Organization of the connections between claustrum and cortex in the mouse

The Social Behavior Network

Part Of: Affective Neuroscience sequence
Content Summary: 800 words, 8 min read

Primary Emotion

There are many possible emotions. How can we make sense of this diversity?

Primary emotions are often used to shed light on our emotional lives. Like primary colors, these emotions blend together to reconstitute the full spectrum of emotional experience. For example, contempt is viewed as a combination of anger and disgust.

An emotion qualifies as primary if it satisfies the following criteria:

  1. Unique Machinery. It must be localized to specific neural processes.
  2. Known Signature. A fixed set of phenomenological and behavioral expressions
  3. Universal (Pre-Cultural). Expressed in all members of a given species. For ecologically valid stimuli, response does not detract from overall fitness.
  4. Primitive (Pre-Cognitive). Activated more strenuously during early development or immediate crisis (i.e., with minimal cognitive regulation).
  5. Differentiable.  Can be dissociated from other primary emotions.

Despite consensus about the above criteria, there is less agreement on which emotions deserve membership.  Here are three representative lists.

SBN- Theories of Primary Emotions (4)

The Social Behavior Network (SBN)

Neuroscientists studying aggression have identified six brain regions that seem to produce this behavior. They are:

  1. Preoptic Area of the Hypothalamus (PO)
  2. Anterior Nucleus of the Hypothalamus (AH)
  3. Ventromedial Nucleus of the Hypothalamus (VMH)
  4. Periacquductal Gray (PAG)
  5. Lateral Septum (LS)
  6. Extended Amygdala (extAMY)

If any of these regions are damaged, an animal often becomes less aggressive. If you electrically stimulate these regions, the animal becomes enraged.

What is interesting about these six regions is that they were independently discovered by other neuroscientists who labelled them as the seat of parental care.

… AND, by yet other neuroscientists who had been investigating the neural basis of sexual behavior.

What do { Parental Care, Aggression, Sexual Behavior } have in common? They are entirely directed at members of one’s own species. These primary emotions are deeply related to animal social behavior.

Since the six nuclei { PO, AH, VMH, PAG, LS, extAMY } contribute to each of these three emotions & behaviors, they are now called the social behavior network (SBN). 

SBN- Overview

Will it turn out that all social primary emotions are created by the SBN? I don’t know. It is suggestive, however, that Play has been partially localized to the lateral septum (LS).

SBN and Emotion Selection

The SBN is one brain structure that can produce three distinct emotional response. How is this possible? How does each emotion individuate itself within a single apparatus?

To proceed, we consult our “theorizing roadmap”:

SBN- Principles of Structure Function

Conceptually, we are plagued by “too many emotions”. Thus, we can either:

  1. Examine whether our three emotions can be unified; or
  2. Look for granularity within the SBN

Since the former is impractical, let’s look more carefully at the SBN.

One way to explain emotion individuation would be a shape hypothesis. If the intensity of neuron firing is encoded by height, you might expect different topographies (landscapes) to encode different emotions. 

SBN- Emotion Differentiation Shape Hypothesis

Another hypothesis is the granularity hypothesis. This posits that there may be e.g., three subdivisions of the lateral septum, and each subdivision supports a different emotion.

I tend to find this approach more plausible, given my experience with other subcortical structures. That said, time will tell. 🙂

Relation To The Basal Ganglia

The SBN is anatomically related to the basal ganglia. Recall that the basal ganglia has three loops: Associative, Sensorimotor, and Limbic. The SBN is strongly connected to, and shares two nodes with, the Limbic Loop.

SBN- SBN vs Limbic Loop (2)

As we have seen, the basal ganglia is the seat of motivation. The anatomical connection between SBN and basal ganglia mirrors the behavioral link between sociality and motivation. However, on a mathematical level, it is less clear how social emotions can be incorporated into the reinforcement learning apparatus:

SBN- Application to Neuroeconomics

Evolution of Emotion

Let’s use comparative anatomy to discover when the social behavior network evolved. By dissecting brains from five representative species, we can infer that the basal ganglia dates back to at least the origin of ray-finned fish.

SBN- Phylogeny (1)

The SBN nuclei are preserved across our representative species:

SBN- Comparative Anatomy

And hodology (connections) between SBN nuclei are preserved:

SBN- Comparative Hodology

This evidence demonstrates that the social behavior network has been around since the invention of vertebrates. It also raises important questions, such as:

  • How has the SBN changed to support hyper-social animals like primates?
  • How much further back do emotional adaptations go? Do insects feel emotions? If yes, which kinds?

Until next time.

Related Works

  • Newman (1999). The Medial Extended Amygdala in Male Reproductive Behavior: A Node in the Mammalian Social Behavior Network
  • O’connell, Hofmann (2011). The vertebrate mesolimbic reward system and social behavior network: a comparative synthesis

Evolutionary Game Theory

Part Of: Game Theory sequence
Content Summary: 1300 words, 13 min read

Prisoner’s Dilemma Review

The classical Prisoner’s Dilemma has following setup:

Two prisoners A and B are interrogated, and separated asked about one another.

  • If both prisoners betray the other, each of them serves 2 years in prison
  • If A betrays B but B remains silent, A will be set free and B will serve 3 years (and vice versa)
  • If both prisoners remain silent, they will only serve 1 year in prison.

We can express the decision structure graphically:

IPD- Prisoner's Dilemma Overview

We can also represent the penalty structure. In what follows, arrows represent preference. CC → DC is true because, given that B cooperates, A would prefer the DC outcome (0 years in prison) more than CC (1 year).

IPD- Prisoner's Dilemma Regret

Our takeaways from our exploration of the Prisoner’s Dilemma:

  • An outcome is strategic dominance happens when one choice outperforms other choices, irrespective of competitor behavior. Here, DD is strategically dominant.
  • Pareto improvement is a way to improving at least one person’s outcome without harming any other player. Here, DD → CC represents such an improvement.
  • Pareto optimal outcomes are those outcomes which cannot be Pareto-improved.

The Prisoner’s Dilemma shows us that strategically-dominant outcomes need not be Pareto optimal.  Although each arrow points towards the origin for that color, the sum of all arrows points away from the origin.

It packages together the tragedy of the commons, a profound and uncomfortable fact of social living. A person can be incentivized towards an outcome that she, and everybody else, dislikes.

Towards Iterated Prisoner’s Dilemma (IPD)

In the one-off game, mutual defection is the only (economically) rational move. If a person chooses to defect, they will likely receive a bad result.

But consider morwhat happens in a more social setting, where players compete for resources multiple times. An Iterated Prisoner’s Dilemma (IPD) has the following structure:


What strategy is best? Let’s consider two kinds of strategies we might adopt. We can imagine some vindictive prisoners always defecting (AD). Other prisoner’s might be more generous, adopting a Tit-for-Tat (TfT) strategy. This has them initially cooperating, and mirroring their opponent’s previous move.

Let’s imagine that there are 200 “prisoners” playing this game, with each strategy adopted by half of the population. Which strategy should you adopt, in such a scenario?

The games look as follows:

  • AD vs AD: { DD, DD, DD,  … }. After 10 rounds: A has 20 years, B has 20 years.
  • AD vs TfT: { CD, DD, DD,  … }. After 10 rounds: A has 18 years, B has 21 years.
  • TfT vs TfT: { CC, CC, CC, … }. After 10 rounds: A has 10 years, B has 10 years.

These computations can be generalized to n rounds:

IPD- Always Defect vs TfT

The tit-for-tat (TfT) strategy wins because TfT-TfT games are collaborative, but these players also aren’t effectively exploited by players who Always Defect (AD).

Which Kinds of Strategies Are Best?

There is an very large number of possible IPD strategies. Strategy design might include considerations such as:

  • Deterministic vs Mixed. Should we follow logical rules, or employ randomness?
  • Impersonal vs Personal. Do we remember the behavior of each opponent? Do we change strategies given what we know of other players?
  • Fixed vs Adaptive. Should we use our experiences to change the above on-the-fly?

Given this behavioral diversity, which kinds of strategy are most successful?

To answer this question, in 1980 Robert Axelrod conducted a famous experiment. He invited hundreds of scholars to enter an IPD tournament, submitting their agent’s decision algorithm digitally. In a computer simulation, every agent played every other agent 200 times. The agent with highest cumulative utility was declared the winner.

Many agent strategies employed quite complex, using hundreds of lines of code. The surprising result was that simple strategies, including Tit-for-Tat, often proved to be superior. Axelrod described three properties shared among successful strategies:

IPD- Characteristics of Winning Strategy

We can call such strategies instances of reciprocal altruism.

Moral and Emotional Implications

The theory of evolution has shown us that biological systems are the product of an optimization process known as natural selection. Only genes that improve reproductive success win over evolutionary time.

From this context, it has long seemed unclear how human beings (and other animals) came to express altruistic behavior.  W.D Hamilton’s notion of inclusive fitness explains why we behave generously to relatives. As J.B.S Haldane famously joked,

I would willingly die for two brothers or eight cousins.

Game theory explains our behavior towards non-relatives. Specifically,

IPD provides insight into moral cognition. It shows how our selfish genes might, purely for selfish reasons, come to promote behaviors that are (reciprocally) altruistic.

IPD similarly explains certain emotional processes. For example, I have posited elsewhere the existence of social intuition generators like Fairness. We can now explain why natural selection generated such “socially intelligent” mental modules.

Application: Vampire Bats

Instead of jail time, we can modify our outcome structure to be more relevant to biology.

IPD- Ecological Prisoner's Dilemma (1)

Thus, we can use game theory to interpret animals competing for resources. Consider, for example, behavior of the vampire bats.

Vampire bats feed on the blood of other mammals. Their energy budget is such that they can tolerate 2 days of food deprivation before starving to death.

On a given night, 8% of adult vampire bats will fail to find food on a given night. But when they do find food, it is often more than they need.

Of course, these animals have a genetic incentive to share blood within family. But you can also observe bats sharing their food with strangers.

How can selfish genes reward altruistic behavior? Because vampire bats are playing IPD:

  • CC (Reward). I get blood on my unlucky nights. I have to give blood on my lucky nights, which doesn’t cost me too much.
  • DC (Temptation). You save my life on my poor night. But I also don’t have to feed you on my good night.
  • CD (Sucker): I pay the cost of saving your life on my good night. But on my bad night I still may starve.
  • DD (Punishment) I don’t have to feed you on my good nights. But I run a real risk of starving on my poor nights.

Towards Evolutionary Game Theory

To show why altruistic bats are more successful? Yes; we need only invent evolutionary game theory (EGT). Recall how natural selection works:

Individuals with more biological fitness tend to leave more copies of their genes.

EGT simply adds this replicator logic to the Iterated Prisoner’s Dilemma (IPD). Players with higher final scores (most resources) leave more descendants in subsequent populations (image credit):


We saw previously that Tit-For-Tat players outperform those who Always Defect. In EGT, this fact establishes how a gene that promotes altruism successfully invaded the vampire bat gene pool:

IPD- EGT Stable Strategies (2)

Of course, iterated games don’t always have one winner. Consider the following food web (structurally similar to Rock-Paper-Scissors, of course).

Snake beats Fox. Fox beats Hawk. Hawk beats snake.

What if the size of the snake population starts out quite small? In that case, hawks and foxes predominate. Since hawks are prey to foxes, the size of the hawk population decreases. But this means the snakes have fewer natural predators.

The above traces the implications of one possible starting point. However, we can use EGT maths to model the entire dynamical system, as follows (image credit):

IPD- Food Web Rock Paper Scissors (1)

With this image, we can see that any starting point will eventually (after many generations), lead to a (⅓, ⅓, ⅓) divide of snakes, foxes, and hawks. This point is the locus of the “whirlpool”, it is also known as an attractor, or an evolutionarily stable state (ESS).


  • The Iterated Prisoner’s Dilemma (IPD) makes game theory more social, where many players compete for resources multiple times.
  • While one-off PD games favor selfish behavior, IPD can favor strategies that feature reciprocal altruism, such as Tit-for-Tat.
  • More generally, IPD strategies do best if they are nice, retaliating, and forgiving. This in turn explains how certain facets of our social and moral intuitions evolved.
  • Evolutionary Game Theory (EGT) extends IPD by adding replicator logic (more successful strategies are preferentially represented in future generations).
  • Evolutionary Stable States (ESS) encode dynamical attractors, which populations asymptotically approach.

Until next time.

A Dual-Process Theory of Moral Judgment

Part Of: Demystifying Ethics sequence
Content Summary: 900 words, 9 min read


An ethical theory is an attempt to explain what goodness is: to ground ethics in some feature of the world. We have discussed five such theories, including:

  • Consequentialism, which claims that goodness stems from the consequences of an action
  • Deontology, which claims that goodness stems from absolute obligations (discoverable in light of the categorical imperative)

For most behaviors (e.g., theft), both theories agree (in this case, label the act as Evil). But there do exist key scenarios which prompt these theories to disagree. Consider the switch dilemma:

Consider a trolley barreling down a track that will kill five people unless diverted. However, on the other track a single person has been similarly demobilized. Should you pull to lever to divert the trolley?

Ethical Theories- Trolley Problem (2)

Our ethical theories produce the following advice:

  • Consequentialism says: pull the lever! One death is awful, but better than five.
  • Deontology says: don’t pull the lever! Any action that takes innocent life is wrong. The five deaths are awful, but not your fault.

Would you pull the lever? Good people disagree. However, if you are like most people, you will probably say “yes”. 

Things get interesting if we modify the problem as follows. Consider the footbridge dilemma:

Consider a trolley barreling down a track that will kill five people unless diverted. You are standing on a bridge with a fat man. If you push the fat man onto the track, the trolley will derail, sparing the five people.

Dual Process Morality- Trolley Visceral Alternative (1)

Notice that the consequences for the action remain the same. Thus, consequentialism says “push the fat man!”, and deontology says “don’t push!”

What about you? Would you push the fat man? Good people disagree; however, most people confess they would not push the fat man off the bridge. 

Dual Process Morality- Conflicting Judgments (1)

Our contrasting intuitions are quite puzzling. After all, they only thing that’s different between the two cases is how close the violence is: far away (switch) vs up close (shoving).

Towards a Dual-Process Theory

Recall that there are two kinds of ethical theories.

  1. Prescriptive theories describe what goodness objectively is.
  2. Descriptive theories tell us how the brain produces moral judgments.

Consequentialism and deontology are prescriptive theories. However, we can also conceive of consequentialism and deontology as descriptive theories. Let’s call these descriptive variants folk consequentialism and folk deontology, respectively.

Sometimes, people’s judgments is better explained by folk consequentialism; other times, folk deontology enjoys more predictive success. We might entertain two hypotheses to explain this divergence:

  1. Different boundary conditions of a single neural process
  2. Two competing processes for moral judgment

As we will see, the evidence suggests that the second hypothesis, the dual-process theory of moral judgment, is correct.

Dissociation-Based Evidence

Consider the crying baby dilemma:

It’s wartime. You and your fellow villagers are hiding from nearby enemy soldiers in a basement. Your baby starts to cry, and you cover your baby’s mouth to block the sound. If you remove your hand, your baby will cry loudly, and the soldiers will hear. They will find you… and they will kill all of your. If you do not remove your hand, your baby will smother to death. Is it morally acceptable to smother your baby to death in order to save yourself and the other villagers?

Here, people take a long time to answer, and show no consensus in their answers. If the dual-process theory of moral judgment is correct, then we expect the following:

  1. Everyone exhibits increased activity in the dorsal anterior cingulate (dACC). This region is known to reliably respond when two or more incompatible behavioral responses are simultaneously activated. 
  2. For those who eventually choose the folk consequentialist answer (save the most lives) should exhibit comparatively more activity in brain regions associated with working memory and cognitive control.

Both predictions turn out to be true. Here then is the circuit diagram of our dual-process, organized in the two cybernetic loops framework:

Dual-Process Morality- System Architecture

Four other streams of evidence corroborate our dual-process theory:

  • Deontological judgments are produced more quickly than consequentialist ones.
  • Cognitive distractions slow down consequentialist but not deontological judgments.
  • Patients with dementia or lesions that cause “emotional blunting” are disproportionately likely to approve of consequentialist action. 
  • People who are either high in “need for cognition” and low in “faith in intuition”, or have unusually high working memory capacity, tend to produce more consequentialist judgments.

Relation To Other Disciplines

We have previously distinguished two kinds of moral machinery:

  • Propriety frames are a memory format that retains social intuitions.
  • Social intuition generators which contribute to the contents of social judgments.

These machines map to the dual-process theory of judgment. Propriety frames are housed in cerebral cortex, which perform folk consequentialist analysis. Social intuition generators are located within the limbic system, and contribute folk deontology intuitions.

Recall that Kantian deontology attempted to ground moral facts in pure reason (the categorical imperative). While surely valuable as a philosophical exercise, in practice folk deontological judgments have little to do with reason. They are instead driven by autonomic emotional responses. It is folk consequential judgments which depend more on reason (cortical reasoning).

This is not to say that people who prefer consequential reasoning are strictly superior moral judges. But I will address the question which reasoning system should I trust more? on another day.


  • For the switch dilemma, most people reason consequentially (“save the most lives”)
  • For the footbridge dilemma, most people reason deontologically (“murder is always wrong”)
  • These contrasting styles emerge because the brain has two systems of judgment.
  • Folk consequentist reasoning is performed in cerebral cortex.
  • Folk deontology intuitions are generated from within the limbic system.

Until next time.

An Introduction to Ethical Theories

LaPart Of: Demystifying Ethics sequence
Content Summary: 1500 words, 15 min


Ethics discussions can occur at different levels of abstraction. The most concrete ethical discussions involve discussing specific topics; e.g., “is abortion moral”? These scenarios are called applied ethics.

Spend enough time wrestling with applied ethics, and you’ll start wondering what all of these moral intuitions have in common. An ethical theory is an answer to the question “what makes a thing good or bad”?

Meta-ethics answers a yet broader set of questions. What is right and wrong, anyways? Are moral beliefs objectively true in the same sense that the Earth orbits the sun? Or is my condemning an unethical act merely expressing an aesthetic preference (“yuck!”)?

Ethical Theory- Three Abstraction Levels

Image Credit

Today we conduct a whirlwind tour of ethical theories, touching on the most influential theories. Ethical theories are normative: they speak to what moral conclusions ought to be. However, we will see later how these theories also sometimes imperfectly anticipate the emerging science of moral cognition.

We will discuss the following:

  1. Divine Command Theory
  2. Natural Law Theory
  3. Virtue Theory
  4. Deontology
  5. Utilitarianism

The first three theories are the oldest, and have close ties to religious doctrine. The last two are the most well-known theories these days.

Divine Command Theory

Historically, religions have had a good deal to say about right and wrong. One of the oldest ethical theories is Divine Command Theory, which states:

Moral behaviors are those that are commanded (or willed) by the divine.

This theory was originally proposed in the context of Greek mythology. But since it doesn’t say much about the specific character of the divine, it was adopted by Augustine and some (but not all) modern theologians.

One of the strongest criticisms to Divine Command Theory is the Euthyphro Dilemma, which goes as follows:

  • Is an action ethical because God commands it?
  • Or does God command it because it is ethical?

Clearly, we must affirm one of these options. But which one? Either “horn” of the dilemma extracts painful concessions:

  • On the first option, moral content becomes arbitrary. If God changes his mind about moral facts, our moral universe is turned upside down.
  • On the second, God becomes a middleman who conveys independent ethical facts. Why can’t we simply learn moral truths direct from the source?

These days, most philosophers find Divine Command Theory problematic. But there are other ethical theories available to the faithful.

Natural Law

Another approach to ethical theories, championed by Thomas Aquinas, is Natural Law Theory. Moral truths are grounded as follows:

Moral behaviors are those which promote, and do not detract from, a basic good.

A basic good is injected into human nature by God. Here are three such lists, generated by a Catholic, a Muslim, and a philosopher:

Ethical Theories- Natural Law Basic Goods (7)

Ethical actions promote the basic goods; immoral actions detract from the basic goods. This, incidentally, is why Catholics oppose all forms of birth control: they detract from the basic good of Reproduction.

How did these philosophers generate their lists of basic goods? By observing nature. For example, Life and Reproduction usually make the cut because humans naturally prioritize survival and reproductive success (this is a consequence of natural selection).

However, there is a conceptual difficulty in deriving basic goods from nature. This was clearly expressed by Hume’s Law, also called the is-ought gap: what logical procedure could possibly be used to infer normative statements (an “ought”) from descriptive facts of the words (an “is”)?

Virtue Theories

Unlike its competitors, virtue theory doesn’t spend much time telling you what to do (moral behaviors). Instead, people are the subject of moral truths. Behaviors are only good or evil insofar as they enhance or corrupt a person’s character.

Aristotle presented these ideas in Nichomachean Ethics. There he describes ethical behavior as a way to achieve eudaimonia (human flourishing or “the good life”).

A life of eudaimonia is a life of striving. It’s a life of pushing yourself to your limits, and finding success. A eudaimonistic life will be full of the happiness that comes from achieving something really difficult, rather than just having it handed to you.

Aristotle also believed that moral knowledge is learned not by navel-gazing, but instead comes from social interactions. Specifically, good character is developed by spending time with virtuous people. This theory is where the idea of a role model comes from.

So let’s get down to business. In virtue theory, moral facts are grounded as follows:

Moral people are those who have character; that is, they possess basic virtues.

Aristotle identified twelve basic virtues: Courage, Moderation, Flexibility, Cleanliness, Generosity, Ambition, Patience, Truthfulness, Wittiness, Friendliness, Modesty, and Righteous Indignation. A good person nurtures these virtues.

The Golden Mean provides some insight into how these virtues can be refined over time. A person can respond too strongly with a virtue (excess), or too weakly (deficiency). For example, one must not have too much courage, nor too little:

Ethical Theory- Golden Mean (1)

Virtue ethics is surprisingly robust to philosophical criticism. However, one scientific concern has been gaining traction recently. Empirical research in the field of situational psychology increasingly suggests that there is no such thing as character traits.

Make no mistake, seeing vices and virtues in others is a universal human instinct. But there is no guarantee that mental software works correctly (e.g., see how the brain lies to itself about visual experience). And the fact of the matter is, character information contributes zero predictive power over how a person will respond to a given situation.

Duty Theories

The first ethical theories that isn’t explicitly theistic, Immanuel Kant’s deontological (“knowledge of what is proper”) system purports to result from pure reason.

Moral behaviors are those which obey the categorical imperative.

For Kant, the categorical imperative is a procedure by which a person can discover the rigid contents of the moral universe. He presents four perspectives that independently arrive at these moral truths; the two most influential of which are:

  1. The universalizability principle instructs us to act only if you also desire that your action should become a universal law. Lying is wrong because if lying becomes universalized, meaningful communication becomes impossible.
  2. The principle of humanity instructs us to act in such a way that you treat humanity (both yourself or someone else), always also as an end and never simply as a means. This principle underlies the modern idea of human rights, and is leveraged by Nozick’s brand of libertarianism. 

The categorical imperative promotes a kind of moral absolutism: if actions are right or wrong intrinsically, their moral status is invariant to the consequences of an action. And this inflexibility can produce counterintuitive judgments.

For example, consider a house shielding a Jewish family from the Nazis. If a soldier comes to the door asking about its residents, most of use think it would be morally acceptable to lie. Kant, however, claims that lying is wrong in all situations, even ones such as these.

Consequentialist Theories

Deontological theories are invariant to behavioral outcome. But there are many moral situations where outcome seems to matter. Consider the trolley problem, where a trolley is currently barreling down a track and should kill five people unless diverted. However, on the other track one person has been similarly demobilized:

Ethical Theories- Trolley Problem (1)

Kant would say that pulling the lever is simply murder. That five people die is regrettable, but their death does not incriminate the person at the switch. If the person does divert the trolley, the guilt of the single person’s death is on his head.

However, most people think that the number of deaths – the consequence of an action – matters. Consequentialist theories make this intuition explicit:

Moral behaviors are those that bring the most good to the most people.

Consequentialist theories vary on how they define “the most good” (personal well-being) and “the most people” (societal well-being). 

For example, classical utilitarianism, advocated by Jeremy Bentham and John Stuart Mill, which takes the following stances:

  1. Personal well-being originates from hedonism: actions are moral if they increase pleasure and/or decrease pain.
  2. Societal well-being is taken as the sum total of the well-being of constituent individuals.

Many people condemn utilitarianism for its hedonism (“don’t immoral behaviors often feel pleasurable?”). However, this criticism loses some of its force when you remember to distinguish higher pleasures (eg., aesthetic experience) versus baser pleasures. 

The problem of figuring out societal well-being, how to optimize outcomes for communities, is much more challenging. The repugnant conclusion, aka the mere addition paradox, is a particularly damning criticism. A large society with barely tolerable quality of life (e.g., urban sweat shops) doesn’t feel morally equivalent to happier, smaller societies. 

Ethical Theories- Repugnant Conclusion

Thus, maximizing total well-being may be problematic. But different problems emerge if we instead optimize against average well-being. To this day, designing aggregation functions to compute societal well-being remains an essentially unsolved problem.


Today, we discussed the following theories:

Ethical Theories- Summary

There exist other theories besides these, of course. For example, Hobbes’ contractualism makes important contributions to the conversation. 

To date, no ethical theory has emerged as a clear favorite. A recent survey of professional philosophers reveals considerable support for three of the above theories:

Ethical Theories- Philosopher Opinions

Next time, we will explore the interaction between these normative theories and the descriptive science of moral cognition. Until then.