120 J.J. Haldane
me recall the first of the five ways, which St Thomas describes as ‘the most
obvious’. As we saw earlier, this involves the fact that there are changes and
the claim that ultimately these can only result from an unchanging cause of
change. The argument involves an analysis of change in terms of the trans-
ition from potentiality to actuality, and the principle that this can only be
brought about by something that is already actual:
what makes things changeable is unrealized potentiality, but what makes them
cause change is their already realized state: causing change brings into being
what was previously only able to be, and can only be done by something which
already is. For example, the actual heat of fire causes wood, which is able to be
hot, to become actually hot, and so causes change in the wood.The example of wood being heated is offered as an illustration (not
a proof ) of the analysis of change but it is easily misinterpreted in a way
that suggests a rapid rejection of the argument. Generalizing from what
Aquinas writes, one might think that his claim involves the principle
that anything that comes to acquire some feature, comes to acquire it from
something that already possesses that very feature – as the wood is made
hot by the heat of the fire [ (∀x) (∃y) (if x comes to be F, then y is F and
y makes x to be F) ]. The problem, then, is that it seems very easy to refute
this principle by counter-example. A comedian may cause amusement in his
audience without himself being amused; a colourless liquid may stain a
surface green, and so on.
As a general principle of interpretation one should be hesitant to ascribe
silly mistakes to clever thinkers, so if at first they seem to have made an
elementary error one should look more closely. That policy encouraged another
interpretation of the supposed quantifier fallacy in the third way and here
again it suggests a better reading of Aquinas. Prior to the example he writes
‘causing change... can only be done by something which already is’ and
this yields the principle ‘anything that comes to acquire some feature comes
to acquire it from something that already exists and (by implication) has
the power to produce that feature in others [ (∀x) (∃y) (if x comes to be
F then it comes to be so from the agency of y which has an Fness-producing
power) ]. Being made hot by something that is already hot is an instance of
this but so is being amused by someone who is not himself amused.
This clarification deflects one objection, but in doing so it raises a question
about the character of my argument to the existence of a ‘Prime Thinker’ (see
section 4). This reasoned that the acquisition of concepts by Alice depended
upon the activity of prior concept users, Kirsty and James, which in turn led
to the postulation of an agent whose conceptual power is underived. What
needs to be made clear is that this is not presented as an instance of the