Epicurean free will

by Tim Harding

Epicurus’ philosophy of mind is perhaps best explained in terms of Epicurean physics.  Epicurus was a materialist who thinks that the natural world is all that exists, so his physics is a general theory of what exists and its nature, including human bodies and minds (O’Keefe 2010: 11-12).

Epicureans thought that there are only two things that exist per se – atoms and void.  Atoms are the indivisible, most basic particles of matter, which move through void, which is empty space (O’Keefe 2010: 11-12).  Objects as we know them are compounds of atoms, and their various natures are explicable in terms of the different properties or attributes of their constituent atoms (Baltzly 2016: 02-1).

When Epicurus refers to the ‘soul’ he means what we today refer to as the mind, so ‘mind’ is the term I shall use here.  He identifies the mind with a compound of four types of atoms – air, heat, wind and a fourth nameless substance (Long and Sedley 1987: 14C).  Because the mind is composed of atoms, it must be corporeal – only the void is incorporeal (Long and Sedley 1987: 14A).  The mind is a part of the body (located in the chest), responsible for sensation, imagination, emotion and memory (Long and Sedley 1987: 14A, 14B, 15D).  Other functions belong to the ‘spirit’ which provides sensory input to, and carries out the instructions of the mind throughout the body (Long and Sedley 1987: 14B).

According to O’Keefe (2010: 62-63), another Epicurean argument for believing that mind is corporeal is as follows:

Premise 1: The mind moves the body and is moved by the body.

Premise 2: Only bodies can move and be moved by other bodies.

Conclusion: Therefore, the mind is a body.

Long and Sedley (1987:107) identify Epicurus as arguably the first philosopher to recognise what we now know as the philosophical Problem of Free Will.  This problem is if it has been causally necessary we should act as we do, it cannot be up to us, therefore we cannot be morally responsible for our actions (Long and Sedley 1987: 20A).  On the other hand, Epicurus notes that ‘we rebuke, oppose and reform each other as if the responsibility lay also in ourselves’ [Long and Sedley 1987: 20C(2)].

According to Cicero, ‘Epicurus thinks that necessity of fate is avoided by the swerve of atoms’ [Long and Sedley 1987: 20E(2)].  Baltzly explains this ‘atomic swerve’ as atoms moving a minimal distance sideways, apparently for no reason at all, from time to time.  This swerve from their natural downward motion results in atomic collisions (Baltzly 2016: F2.2-14).  Although this swerve is not explicitly mentioned by Epicurus himself, Cicero writes that:

‘Epicurus’ reason for introducing this theory was his fear that, if the atom’s motion was always the result of natural and necessary weight, we would have no freedom, since the mind would be moved in whatever way it was compelled by the movement of atoms’ [Long and Sedley 1987: 20E(3)].

Lucretius presents an argument that the atomic swerve enables free will (Long and Sedley 1987: 20F).  O’Keefe (2010: 74-75) states this argument in the following form:

Premise 1: If the atoms did not swerve, there would not be ‘free will’.

Premise 2: There is free will.

Conclusion: Therefore, atoms swerve.

This argument is logically valid, so if the premises are true the conclusion must be true.  Lucretius spends most of this passage trying to show that Premise 2 is true.  However, even if Premise 2 is true, we do not know that Premise 1 is true.  The atomic swerve introduces a slight element of indeterminacy, but this swerve does not necessarily entail free will, since no mechanism is given to explain the connection between these two concepts.  Indeed, Annas (1991: 87) argues that there is a fundamental problem in thinking of human motivation in terms of only the motion of atoms.  She thinks that occurrence of atomic swerves in ordinary macro-objects has no effect on them (Annas 1991: 96-97).  For this reason, I do not think that the introduction of random atomic swerves solves the Problem of Free Will.

Sedley (1987: 107) agrees that taken in isolation such a solution is ‘notoriously unsatisfactory’.  He offers an alternative explanation in terms of ‘development’ which contributes psychological autonomy and which is distinct from the atoms in a kind of differential or transcendent way (Long and Sedley 1987: 107-18).  In other words, these distinct developments are psychological rather than physical properties of the mind.  In particular, the development of consciousness which is an ‘emergent’ property of complex atomic systems like human beings (Baltzly 2016: F2.2 – 17).

In a later paper, Sedley provides some more detail on what he means by emergent properties:

‘I take Epicurus to be sketching some sort of theory of radically emergent properties.  Matter in certain complex states can, he holds, acquire entirely new , non-physical properties, not governed by the laws of physics’ (Sedley 1988: 323-324).

It is important to note that Sedley is attempting here to make a connection between free will and the atomic swerve.  As Baltzly (2016: F2.2 – 18) puts it, the swerve means that not every motion of the atoms which make up our bodies is determined by those atoms themselves.  Baltzly thinks that the swerve does not introduce an element of randomness or indeterminacy into our free choices:

‘Rather, the swerve leaves a gap where the psychological properties of my soul [mind] can cause something to happen where behaviour of the atoms that make up my soul [mind] leave it open what will happen’ (Baltzly 2016: F2.2 – 18).

My own view is that Sedley and Baltzly provide a plausible explanation of the connection between Epicurus’ atomic swerve and free will.  It is possible that consciousness is an emergent psychological property of the material mind.  Free will could be seen as a manifestation of consciousness.  Whilst we cannot yet fully explain what consciousness is and how is works, there is little doubt that consciousness exists.  If consciousness can exist, then so can free will.  However, where I part company with Sedley is that I find Epicurus’ theory of the atomic swerve unconvincing.  Neither Epicurus nor his followers provide any evidence for the existence of the atomic swerve.  It has been postulated as a kind of ‘retrofit’ in an attempt to solve the problem of free will by introducing an imaginary element of indeterminacy.  I think that Sedley’s idea of emergence could help to explain free will even in the absence of the Epicurean atomic swerve.

I would now like to draw towards a conclusion about Epicurus’ philosophy of mind, by comparing it with the theories of his competitors.  According to O’Keefe (2010: 80-83), these were mainly Carneades (214-129BCE) the head of the skeptical academy; and Chrysippus (c.280-206BCE) the third head of the Stoic school.

The most relevant criticism of Carneades is that positing a motion without a cause, like the atomic swerve, would be beside the point in solving the problem of free will (O’Keefe 2010: 82).  Carneades’ solution is to say that all events, including human actions, have causes   These actions are the result of ‘voluntary motions of the mind’ rather than external causes.  He thinks that there is no reason to posit, in addition, a fundamental indeterminism like the atomic swerve (O’Keefe 2010: 82).  In this way, Carneades was perhaps the forerunner of a compatibilist solution to the problem of free will, allowing both determinism and voluntary choices to co-exist.

Chrysippus criticises Epicurus from the opposite direction.  He shows that causal determinism does not make the future inevitable in a manner that renders action or deliberation futile.  In this way, determinism is compatible with human agency (O’Keefe 2010: 82).

In conclusion, I think that Sedley, Carneades and Chrysippus have pointed the way towards a compatibilist solution to the problem of free will, that does not depend on the dubious Epicurean postulation of the atomic swerve.  I therefore think that their approaches to this problem are more compelling than those of Epicurus.


Annas, J. ‘Epicurus’ Philosophy of Mind’ Companions to Ancient Thought: 2 Psychology, S. Everson, ed. (1991) Cambridge: Cambridge University Press.

Baltzly, D. ATS3885: Stoic and Epicurean Philosophy Unit Reader (2016). Clayton: Faculty of Arts, Monash University.

Long A. A. and Sedley, D. N. The Hellenistic Philosophers, Volume 1 (1987). Cambridge: Cambridge University Press.

O’Keefe, T. Epicureanism. (2010). Berkeley: University of California Press.

Sedley D. ‘Epicurean Anti-Reductionism’ in Jonathan Barnes Mario Mignucci (ed.), Matter and Metaphysics. Bibliopolis 295–327 (1988).

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