Handbook of the History of Logic: - Fordham University Faculty

The Development of Supposition Theory in the Later 12 th through 14 th Centuries 221
say that neither entails the other, but one wants an explanation of the semantics
of the former, if it is not the same as the latter. 71
Buridan argued that by parity, if I promised you a horse, then either every horse
I promised you, or no horse I promised you. He found the latter counter-intuitive,
and so settled on the former. This view was not widely accepted.
Ockham proposes what seems to me to be the right thing to say. He says that
‘I promise you a horse’ means that this ought to be true: ‘I give you a horse’. He
says:
Thus, ‘I promise you a horse’, given the force of ‘I promise’, asserts
that ‘I give you a horse’ (or something similar) will be or ought to be
true sometime. The assertion is not that a proposition like ‘I give you
this horse’ (where the reference is to some particular horse) will be or
ought to be true. Thus, it does not follow that if I promise you a horse,
I promise you this horse or I promise you that horse. [Ockham SL 1.72
(207-08)]
Buridan dismisses this, saying
We should realize that some people, wanting to evade the difficulty
straight away, say that this is not a proper locution: ‘I owe you a
horse’ or ‘A horse is owed by me to you’, but that this locution should
be taken in the sense that ‘I owe or am bound to bring it about that
you have from me a horse’. And so the proposition ‘I owe you a horse’
or ‘A horse is owed by me to you’ is neither true nor false, except in
this sense. 72
But this solution seems to me to be superficial, for there are several
ways in which [it can be arranged that] this can be brought about: for
one way to bring this about would be to give you Blackie, and another
way to bring this about would be to give you Tawny. Therefore, the
question would recur whether I would be bound to do so in every such
way or whether I would be bound to do so in no such way. [Buridan
SD 9.4 Fifteenth sophism (912)]
It is difficult to assess Buridan’s criticism, for it seems to miss the mark. His
objection is that the proposal does not settle the question of whether to fulfill the
obligation I must give you every horse, or no horse. But the proposal seems to be
that giving a single horse satisfies the obligation, and any one will do.
Much intricate discussion of this example continued throughout the 15th century
and beyond. For more information, see Ashworth [1974; 1976].
71 Most writers agreed that ‘horse’ in the latter proposition has determinate supposition, since
it is equivalent to ‘This horse I promised you, or that horse I promised you, or . . , and so on
for all horses.” (See chapter 8 for a discussion of determinate supposition.) Many wanted to say
that ‘horse’ in the former proposition has merely confused supposition; this will be discussed in
chapter 8.
72 For discussion of this “evasive move” by Ockham, as well as in contemporary logic, see [Read,
1985; Biard, 1988; Klima, 1993].