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A9. The Megarian challenge

Aristotle himself has to defend his theory of dispositions against an alternative position put forward by a group of philosophers called “Megarians” that has some similarities with Hartmann's account of total possibility.[1] Aristotle describes this position as follows:

There are some who say, as the Megarians do, that a thing can act only when it is acting, and when it is not acting it cannot act, e.g. that he who is not building cannot build, but only he who is building, when he is building [...]. (Met. IX 3, 1046a 29-32)

The Megarians, that is, regard the realisation of something both necessary and sufficient for having the disposition for doing this: x has a disposition to do or to be F at t if and only if x is actually F at t. Aristotle formulates no less than four arguments against this position showing which strange conclusions (atopa, 1046a 33) such a position would entail:

(1) Learning a craft is different from (and more difficult than) merely switching from non-employing to employing a craft. If the builder would not have any building disposition when not building, there would be no difference between a non-building builder and someone who is not a builder at all.

(2) Also, there would be no difference between a thing being perceivable and that thing being perceived (and Protagoras would be right), for then a thing would be perceivable if and only if it would actually be perceived.

(3) Also, people would frequently become blind and deaf when closing their eyes or entering a silent room.

(4) Finally, Megarians do away with change and becoming (and Parmenides rejoices) because if there is no principle of change to become something not yet existing, nothing can ever come into existence that is not yet present.[2]

To be sure, none of the strange consequences makes it necessary for the Megarians to withdraw their claim. They could as well (and maybe they did) embrace the Parmenidean and Protagorean implications. However, any philosopher who, like Aristotle, sees some value in common-sense opinions and rejects positions that are more revisionary than necessary has plenty of reasons to reject the Megarian claim. This is the lesson Aristotle learns from the discussion of the Megarian position. Contrary to the Megarian claim, terms for the possession of a disposition and terms for their respective realisation usually have different extensions. This is possible because, as a rule, dispositions are “two-sided”: It is possible to have a disposition and not realise it at the same time.

Therefore, it is necessary to distinguish between the time at which something has a disposition and the time for which this disposition allows a realisation. At daytime an owl already possess the disposition to realise an enormous visual perception when it is dark at night. Here, daytime is the at-time, i.e. the time at which the owl has that disposition, whereas the night is the for-time,

i.e. the time for which that disposition allows a realisation.

Disposition ascriptions in natural language contexts normally do not contain any reference to a for-time. Thus, it should come as a surprise that some criticise such an analysis because “it does not make sense to speak of a capacity for standing-at-t, but only for standing”.[3] But there is help on the way: We can get rid of the for-time without falling back in the Megarian mess. The syntactical trick that I will employ is to turn the free variable that the reference to the for-time has been in our previous formulations into a bound variable. The ontological idea behind this is that as a relevant causal factor for its realisation, a disposition precedes its effect. Thus, the realisation of a hitherto unrealised disposition could happen at some time in the future given that the disposition does not get lost in between. Hence, if something has at t a disposition to do or to be F, this disposition at least allows its bearer to display the realisation of F at some t* immediately after t. This means that we interpret a dynamis as a causal factor that precedes its effect and may (but need not) be co-present with its realisation.

  • [1] On the attempts to identify these philosophers cf. section 4.1.1
  • [2] For a formal account of this last argument cf. section 4.1.3
  • [3] Waterlow 1982, 40
 
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