Last year during the big lockdown I pre-filmed all of my logic lectures for the university where I work. Here is the playlist. If you get through all of it then you will know a lot about propositional and predicate logic (with identity). Once you know the latter you will know pretty much everything that you need to know to go and teach yourself most logics out there (there are lots of different logics).

Post Q's in this thread and I shall answer them as soon as I can. I am a little busy with things but shall check in regularly.

I should warn that these vids are insanely home baked as I had no idea what I was doing with the camera. Still, I used them to teach over 1100 students (really) logic last year, so they work. edit - there are 22 videos in this playlist, so it's a deep dive.

This is fantastic. Thanks so much. Shall get stuck in.

So great, thanks for this! I need a reminder...

Gonna dive into this when I get a good stretch of quiet time. Thanks Seb!

1. All men are mortal.
2. Socrates is a man.
3. Ipso facto, all men are Socrates.

Anonymous37 wrote: Thu May 06, 2021 2:05 pm 1. All men are mortal.
2. Socrates is a man.
3. Ipso facto, all men are Socrates.

Ahhhhh no! The conclusion (3) does not follow from the premises (1) and (2).

The first premise states that if you take the total collection of mortal things, then the total collection of men will be included in this collection of mortal things.

The second premise states only that one of these men is Socrates.

So, what follows from this is that Socrates is mortal, since he is one of the men, and all of the men are mortal.

The claim that all men are Socrates does not follow from the premises. In fact it is consistent with the premises that plenty of men are not Socrates.

Looking ahead - there will be models where both the premises and your conclusion are true (a model whose domain contains only one object), but there will also be models where both the premises are true and the conclusion false (any model where the domain contains more than one object). A valid argument is one for which there is no model where all of the premises are true and the conclusion false. Hence your argument above is invalid.

But this is predicate logic and we do not get there until we are in deep!

I am 100% certain that FM seby picked his profession based on his own looks.

^ Thank you for noticing : )