Handbook of the History of Logic: - Fordham University Faculty

The Development of Supposition Theory in the Later 12 th through 14 th Centuries 219
Nowadays, our instinct would be to deny the first premise. We would be inclined
to say that we do know the one approaching. Granted, we don’t know who the
one approaching is, but this is a different claim. Thus the puzzle is easily solved.
However, this was not the medieval approach. 69
One solution offered by Buridan and several of his followers was to say that
certain mental verbs relate one thing to another, not absolutely, but in relation
to a ratio. You can be said to know A if you know A under the ratio A. If B is
the same as A, then it does not follow that you know B, for this requires that you
know B under the ratio B. And the identity of A with B does not guarantee that
the ratio A is the same as the ratio B. This solves the puzzle, since:
You know your father under the ratio your father.
Your father is the one approaching.
You can legitimately conclude:
You know the one approaching under the ratio your father.
But you cannot conclude:
You know the one approaching under the ratio the one approaching.
There is thus a kind of de dicto construal of the locution ‘know ’. There is also
a de re wording; it is the one in which the term that supposits for the known thing
precedes the verb. In this case there is the analysis:
X you know = you know X under some ratio
So these are both true:
You know your father
Your father you know (You know your father under some ratio.)
(The first is taken to be data. The first entails the second, because it entails
You know your father under the ratio your father.)
And if you know the one approaching, this also is true:
The one approaching you know.
But none of this lets you conclude:
You know the one approaching.
What, then, is a ratio? This is not clear, but it would be natural to take the
ratio associated with a term to be the mental concept that the term is imposed
on. That would legitimate the above solution.
69 Nor is it clear whether it avoids the problem. For we now face a related puzzle: “You
don’t know who the one approaching is. The one approaching is your father. So apparently you
don’t know who your father is.” One can interpret the medieval theorizing as about this latter
formulation.