The Logic Forum Discussion Area

Start a New Topic 
View Entire Thread
Re: FUTURE LOGIC - Comments & Queries


In the first figure, the 'all circumstances' of the minor premises are those applicable to the minor term S, they are not all circumstances concerning the middle term M. For this reason, there is no guarantee that the 'some circumstances^concerning M in the major premise are covered.

On the other hand in the third figure, M being the subject in both premises, you can be sure of overlap of circumstances.

Best, Avi.

Something about you (optional) logician-philosopher

Re: FUTURE LOGIC - Comments & Queries

Thanks Avi, for some reason I just wasn't getting it. I think I was confusing myself by reading the premises as "all S in all circumstances is what P is in some circumstances". I was looking at the quantity and not the modality. Then I drew a diagram to represent the circumstances "surrounding" the terms. Being more of a visual thinker, the invalidity then became clear.

But still, some of these modal syllogisms aren't at all obvious.

Re: FUTURE LOGIC - Comments & Queries

In fig. 1, if you tried converting the minor premise, you would have immediately seen that while S was distributed, M was not. All S must be M converts to Some M can be S. Remember All S means: Each S - it is distributive, not collective or collectional. So, the all circumstances are all circumstances concerning each S, which are not the same set of circumstances... The universal proposition is a mere summary formula.

Note additionally that in the past, some logicians thought that a universal potential major premise in the first fig. could yield a valid conclusion. They did not realize the issues involved. So, you are in good company!

Something about you (optional) logician-philosopher