How, in Aristotle's view, can thought cause action?
How, on occasion, may it fail to cause action?

The essay's title question inquires about how, in Aristotle's theory of human psychology, the thought processes that constitute a deliberation about the proper thing to do connect to the action that is supposed to result from such a deliberation.  As such, the title question is focussed on Aristotle's theory of the "practical syllogism" and the role played by his explanation of "akrasia" (weakness of will).

According to Aristotle there is a distinctive mode of thinking that underlies ethics - practical intelligence or prudence (also referred to as practical reasoning).  This faculty alone understands the true character of individual and community welfare and applies its results to the generation of human action.  Acting properly, in Aristotle's theory, involves coordinating our desires about the correct goals or ends with correct thoughts about the practical means of attaining them.  The role of deliberative reasoning is to consider each of the many actions that are within one's power to perform, and consider the extent to which each of them would contribute to the achievement of the appropriate goal or end, resulting in a deliberated choice to act in the way that best fits that end.

"moral virtue is a state of character concerned with choice, and choice is deliberate desire, therefore both the reasoning must be true and the desire right, if the choice is to be good" (NE 6.2)

It might be thought that the best means of understanding just how Aristotle believed that thought causes action would be to collect and examine the various examples of "practical reasoning" that he offers throughout his works.  Unfortunately, however, none of the examples he offers appear to share a consistent structure, and the differences between them are often greater than the similarities.  As a result, the exact nature of Aristotle's theory in this regard is open to considerable debate.  Even which passages constitute examples, and hence the number of relevant examples, is a matter of considerable debate.

The passages relevant to an understanding of Aristotle's practical syllogism occur in two separate contexts.  The first is in the ethical context -- the Nicomachean Ethics, the Eudemian Ethics, and the Magna Moralia.  It is in these works that he discusses "practical reasoning" and how it guides human action.  The other context is psychological - his De Motu Animalium (Chapter 7) and De Anima (III.10).  It is in these latter two works that Aristotle's discusses how the soul moves the body.

Focussing just on the ethical works, one might be led to conclude that the practical syllogism is a process of logical deduction from major and minor premises to a conclusion after which there is action.  But such an interpretation does not resolve the question of just how it can be that logical thought can result in action.  To address that question, one must also consider the psychological context.

There are a number of places where Aristotle is very clear that the process of deliberation ends with a choice of what is judged the right thing to do under the circumstances.  Virtuous or appetitive desire for the ends or goals of thought, and deliberation as to the proper means to that end combine with the perception of the proper circumstances to initiate the action conclusion of the practical syllogism.  "Virtue makes the goal right, practical wisdom the things leading to it" (NE 7.12).  Deliberation is the first part, the practical syllogism is the final part.  The psychological process that proceeds from this judgement and ends with actual action is separate.

In a number of places (especially in his De Motu Animalium where he deals with action initiation in animals), Aristotle goes into detail as to how this process of action initiation works.  His descriptions of this bit of psychology make use of the same terminology he uses in his descriptions of the logical syllogism.  So successors to Aristotle have come to call his process of action initiation the "practical syllogism".  However, Aristotle himself never applies that term to the process.

Aristotle describes the practical syllogism as including a universal premise, a particular premise which is perceived and not thought, and a conclusion that is an action

"For the one premise is a universal belief, and the other concerns particular things, for which perception is decisive. Whenever one belief follows from others, the soul must in the one case affirm the conclusion, but in practical affairs it must enact it immediately." (NE 7.3)

"the one premise or judgement is universal and the other deals with the particular (for the first tells us that such and such ia kind of man should do such and such a kind of act, and the second that this is an act of the kind meant, and I am a person of the type indicated)". (De Anima 434a15-20)

The universal or major premise comes from education, (virtuous) habit, observation, and example, from an educated sense of what eudaimonia means in these circumstances and the variously ranked goods of life.  The particular or minor premise comes from a perception of the particular circumstances.  The conclusion is the proper action.  When one comprehends or combines the two premises in a practical syllogism, one acts at once (assuming one is able and not forced or prevented).  There is, however, significant debate whether Aristotle believed that people actually think in a logical process, or is merely providing a description of how the psychology works as if it were a logical process. 

What provides the connection between the premises and the action comes from a combination of practical (rather than theoretical) reason and want, desire, wish, or appetite.  These two combine to initiate an action for the sake of something, in pursuit of some end.  An action is the means by which we seek to satisfy an appetite.  Practical reason informs the appetite by advising which action is the most appropriate means to the desired end.

"Both of these then are capable of originating local movement, mind and appetite: (1) mind, that is, which calculates means to an end, i.e. mind practical (it differs from mind speculative in the character of its end); while (2) appetite is in every form of it relative to an end: for that which is the object of appetite is the stimulant of mind practical; and that which is last in the process of thinking is the beginning of the action." (De Anima III.10)

On the one hand, Aristotle claims that both practical reason and desire or want are required to motivate any action for the sake of something.  But on the other, it appears he also claims that appetite can produce action on its own.

"That which moves therefore is a single faculty and the faculty of appetite; for if there had been two sources of movement-mind and appetite - they would have produced movement in virtue of some common character. As it is, mind is never found producing movement without appetite . . ., but appetite can originate movement contrary to calculation, for desire is a form of appetite." (De Anima, III.10)

So it would appear that thought (in the form of practical reason) is not sufficient of itself to cause action.  It must be accompanied by a want, desire, wish, or appetite.  For it is the want of something that motivates us to action in order to satisfy that desire.  Thought can only inform the appetites of the most suitable means to satisfy the appetite.  Thought without appetite cannot cause action.

This disconnect between the thoughts of practical reason, and the motivating force of the appetites provides the opening that Aristotle requires to explain why it is that practical reason sometimes fails to elicit the action that is judged the best.  Consider these two examples that Aristotle provides of the practical syllogism in action -

Example 1:-

Universal Premise 1: "Everything sweet ought to be tasted"

[Universal Premise 2: "Sweet things are pleasant"]  -  "hidden" premise

Particular Premise / Perception: "This is Sweet"

Conclusion / Action: "This is tasted"


Example 2:-

Universal Premise 1: "Sweet things ought to be avoided"

[Universal Premise 2: "Sweet things are pleasant"]  -  "hidden" premise

Particular Premise / Perception: "This is Sweet"

Conclusion / Action (a): "This is avoided"

Conclusion / Action (b): "This is tasted"

In example 1, we have the first universal premise that is the output of a process of deliberation.  The second universal premise we can treat as if contributed by the appetites, since it is the result of the experiences of the appetites.  The particular premise, Aristotle maintains is the result of perception.  The conclusion that follows is the action of tasting.  Here in this example, we have a case where the thought "Everything sweet ought to be tasted" causes the action of tasting by way of the perception "This is sweet" and the appetitive motivator that "Sweet things are pleasant".

In example 2 we have again the first universal premise that is the output of deliberation.  In this case, perhaps as a consequence of considering the detrimental health consequences of overindulgence in sweets, the conclusion of the deliberation is that sweets ought to be avoided.  If the result of the practical syllogism is the action that the sweet is avoided, then the thought has been successful in causing the (in)action.  But if the result of the practical syllogism is that the sweet is tasted, then the thought has failed to cause the (in)action.

In his discussion of akrasia in Chapter 7 of the Nicomachean Ethics, Aristotle explains the failure of thought to cause action as the result of either of two effects.  One possible source of failure is that the universal premise that starts the process might encode a thought about an end that cannot be realized in these circumstances.  There is a lack of an accompanying appetite, there is no want for the end that is the subject of the thought.  The other possible source of failure is that the premise provided by reason is overwhelmed by the premise provided by the appetites.  The first case, Aristotle describes as a matter of ignorance or "intellectual error".  The individual thinking about action is ignorant of the fact that the circumstances do not permit action in pursuit of the end in mind because there is no desire for the end in mind.  The second case, Aristotle describes as a matter of weakness of will.  The individual in question has had improper or insufficient moral training, and is allowing his appetites to overrule his reason.  In providing two different explanations for why practical reason might fail to control the appetites, Aristotle distinguishes between "drunk akrasia" and "genuine akrasia".  

Aristotle describes two different senses of how a person can "know" things.  There is the passive sense in which it can be said that the geometer "knows" the axioms of Euclid, even when he is asleep, or distracted by other interests, or drunk and incapable (hence the label "drunk-akrasia").  And there is the active sense in which the geometer can be said to know those axioms while he is actively employing them in his labours.  So the drunk-akratic man can be said to "know" that the end that is the subject of his though is undesired in the passive sense, while it can also be said that he does not "know" it to be undesired in the active sense. 

In the process of deliberation leading up to the universal premise of the practical syllogism, the akratic man may fail to consider whether his current situation falls under one of the means-ends routes he has chosen by prior deliberation, or misevaluates the likely consequences in a current deliberation due to ignorance or inattention, or has allowed his passions to cloud his judgement as a drunk has allowed the drink to cloud his judgements.  In the passive sense, then, the "drunk-akratic" man does not know (in the active sense) that the subject of his thought is inappropriate, and (at least at the moment) believes that what he is thinking is right.  Only later, when his rational soul recovers, does the recognition dawn that he was mistaken and should have known better.  With the recognition that he erred, and should have done better, comes the pain and regret that Aristotle claims is the mark of action out of ignorance.

This explanation does not serve for the "genuine-akratic" man, however.  The genuine akratic man mirrors the deliberations that mark the virtuous or temperate man.  Yet he still habitually yields to those pleasures of vice.  Aristotle's best explanation of this situation is derived from his concept of "proper pleasures" and the nature of "proper moral training".  What the genuinely-akratic man is lacking is the proper training of his appetites in an appreciation of the "proper pleasures" of temperance.  The virtuous man has been so trained that his appetitive soul does not "see" the pseudo-pleasures of the vices.  So the virtuous man does not experience any conflict between the thoughts of reason and the motivations of appetites.

So, thought causes action through the interaction in the practical syllogism of the rational soul that deliberates about means to ends, and the appetitive soul that desires and fears.  The failure of thought to cause action arises in two ways.  One is the failure of the deliberative part of practical reasoning to choose a means to an end that is desirable.  The absence of a desire for the end being pursued by the universal premise of the practical syllogism means that there will be no action initiated.  The second is the overwhelming of the universal premise resulting from practical reasoning by the hidden premise of the desires.  It is the lack of adequate moral training of the appetites that results in a conflict between the prescriptions of rational thought, and the desires of the appetites.  In particular it is the failure of the appetites to appreciate the proper pleasures of temperance that generates the conflicts that sometimes result in the failure of rational thought to cause action. 


From the Nicomachean Ethics, Book 7, Chapter 3:

"The one opinion is universal, the other is concerned with the particular facts, and here we come to something within the sphere of perception; when a single opinion results from the two, the soul must in one type of case affirm the conclusion, while in the case of opinions concerned with production it must immediately act (e.g. if 'everything sweet ought to be tasted', and 'this is sweet', in the sense of being one of the particular sweet things, the man who can act and is not prevented must at the same time actually act accordingly). When, then, the universal opinion is present in us forbidding us to taste, and there is also the opinion that 'everything sweet is pleasant', and that 'this is sweet' (now this is the opinion that is active), and when appetite happens to be present in us, the one opinion bids us avoid the object, but appetite leads us towards it (for it can move each of our bodily parts); so that it turns out that a man behaves incontinently under the influence (in a sense) of a rule and an opinion, and of one not contrary in itself, but only incidentally-for the appetite is contrary, not the opinion-to the right rule."

From De Anima, Book III, Chapter 10

"These two at all events appear to be sources of movement: appetite and mind (if one may venture to regard imagination as a kind of thinking; for many men follow their imaginations contrary to knowledge, and in all animals other than man there is no thinking or calculation but only imagination).

"Both of these then are capable of originating local movement, mind and appetite: (1) mind, that is, which calculates means to an end, i.e. mind practical (it differs from mind speculative in the character of its end); while (2) appetite is in every form of it relative to an end: for that which is the object of appetite is the stimulant of mind practical; and that which is last in the process of thinking is the beginning of the action. It follows that there is a justification for regarding these two as the sources of movement, i.e. appetite and practical thought; for the object of appetite starts a movement and as a result of that thought gives rise to movement, the object of appetite being it a source of stimulation. So too when imagination originates movement, it necessarily involves appetite.

"That which moves therefore is a single faculty and the faculty of appetite; for if there had been two sources of movement-mind and appetite-they would have produced movement in virtue of some common character. As it is, mind is never found producing movement without appetite (for wish is a form of appetite; and when movement is produced according to calculation it is also according to wish), but appetite can originate movement contrary to calculation, for desire is a form of appetite. Now mind is always right, but appetite and imagination may be either right or wrong. That is why, though in any case it is the object of appetite which originates movement, this object may be either the real or the apparent good. To produce movement the object must be more than this: it must be good that can be brought into being by action; and only what can be otherwise than as it is can thus be brought into being. That then such a power in the soul as has been described, i.e. that called appetite, originates movement is clear. Those who distinguish parts in the soul, if they distinguish and divide in accordance with differences of power, find themselves with a very large number of parts, a nutritive, a sensitive, an intellective, a deliberative, and now an appetitive part; for these are more different from one another than the faculties of desire and passion."

From De Motu Animalium, Chapter 7 -

"But how is it that thought (viz. sense, imagination, and thought proper) is sometimes followed by action, sometimes not; sometimes by movement, sometimes not? What happens seems parallel to the case of thinking and inferring about the immovable objects of science. There the end is the truth seen (for, when one conceives the two premisses, one at once conceives and comprehends the conclusion), but here the two premisses result in a conclusion which is an action — for example, one conceives that every man ought to walk, one is a man oneself: straightway one walks; or that, in this case, no man should walk, one is a man: straightway one remains at rest. And one so acts in the two cases provided that there is nothing in the one case to compel or in the other to prevent. Again, I ought to create a good, a house is good: straightway I make a house. I need a covering, a coat is a covering: I need a coat. What I need I ought to make, I need a coat: I make a coat. And the conclusion I must make a coat is an action. And the action goes back to the beginning or first step. If there is to be a coat, one must first have B, and if B then A, so one gets A to begin with. Now that the action is the conclusion is clear. But the premisses of action are of two kinds, of the good and of the possible.

"And as in some cases of speculative inquiry we suppress one premise so here the mind does not stop to consider at all an obvious minor premise; for example if walking is good for man, one does not dwell upon the minor 'I am a man'. And so what we do without reflection, we do quickly. For when a man actualizes himself in relation to his object either by perceiving, or imagining or conceiving it, what he desires he does at once. For the actualizing of desire is a substitute for inquiry or reflection. I want to drink, says appetite; this is drink, says sense or imagination or mind: straightway I drink. In this way living creatures are impelled to move and to act, and desire is the last or immediate cause of movement, and desire arises after perception or after imagination and conception. And things that desire to act now create and now act under the influence of appetite or impulse or of desire or wish."


Aristotle; The Nicomachean Ethics (Oxford World Classics), Oxford University Press, Oxford, England. 1980. ISBN 0-19-283407-x.

Aristotle; "The Eudemian Ethics", in Aristotle in 23 Volumes, Vol. 20, translated by H. Rackham. Cambridge, MA, Harvard University Press; London, William Heinemann Ltd. 1981. The Perseus Digital Library, Tufts University, URL=

Aristotle; "Magna Moralia" in The Works of Aristotle, translated by W.D.Ross; Oxford University Press / Clarendon Press, London England, 1915; The Internet Archive, URL=

Aristotle; De Anima; Translated by A.J.Smith. The Internet Classics Archive. URL=

Aristotle; Aristotle's De Motu Animalium: Text With Translation, Commentary, and Interpretive Essays, Princeton University Press, Princeton, New Jersey, 1978. ISBN 978-0691072241.

Aristotle; Politics (Oxford Worlds Classics), Oxford University Press, Oxford, England. 2009. ISBN 978-0199538737.

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