Prior Analytics - Book I   

A's possibility (and A is assumed to be possible), consequently B will

be possible: for if it were impossible, the same thing would at the

same time be possible and impossible.

Since we have defined these points, let A belong to all B, and B

be possible for all C: it is necessary then that should be a

possible attribute for all C. Suppose that it is not possible, but

assume that B belongs to all C: this is false but not impossible. If

then A is not possible for C but B belongs to all C, then A is not

possible for all B: for a syllogism is formed in the third degree. But

it was assumed that A is a possible attribute for all B. It is

necessary then that A is possible for all C. For though the assumption

we made is false and not impossible, the conclusion is impossible.

It is possible also in the first figure to bring about the

impossibility, by assuming that B belongs to C. For if B belongs to

all C, and A is possible for all B, then A would be possible for all

C. But the assumption was made that A is not possible for all C.

We must understand 'that which belongs to all' with no limitation in

respect of time, e.g. to the present or to a particular period, but

simply without qualification. For it is by the help of such

premisses that we make syllogisms, since if the premiss is

understood with reference to the present moment, there cannot be a

syllogism. For nothing perhaps prevents 'man' belonging at a

particular time to everything that is moving, i.e. if nothing else

were moving: but 'moving' is possible for every horse; yet 'man' is

possible for no horse. Further let the major term be 'animal', the

middle 'moving', the the minor 'man'. The premisses then will be as

before, but the conclusion necessary, not possible. For man is

necessarily animal. It is clear then that the universal must be

understood simply, without limitation in respect of time.

Again let the premiss AB be universal and negative, and assume

that A belongs to no B, but B possibly belongs to all C. These

propositions being laid down, it is necessary that A possibly