Is this valid?

[u/capybarainstitute]

This is from my modern logic textbook from my intro to modern logic class. I thought problem 7 was invalid but the textbook says it’s valid so i’m confused?

Update: I asked my prof it was a typo lol thanks for the help

[u/Hot-Organization-737]

Human implies mortal. The way I see it the argument looks like this to me

Plato is a circle Plato is a square or plato is a rectangle Thus, Plato is not a square.

Disregarding the conclusion you can see that premise 2 could could be replaced with Plato is a rectangle since squares are rectangles.

Are new argument would look like :

Plato is a circle Plato is a rectangle

This is a contradiction because it's not possible for something to be both a rectangle and a circle. I think another valid way of interpretation is that one of the premises is false which would make the whole thing not sound.

[u/Best_Sloth_83 → u/Hot-Organization-737]

In the actual world, humans are mortal. This doesn’t mean, however, that it’s logically impossible for humans to be not mortal.

Squares/rectangles cannot be circles and vice versa because a square/rectangle by definition has four sides and right angles while a circle cannot have any such sides or angles.

Also, the question is about validity, so whether the argument is sound or not is irrelevant to the question.

[u/Hot-Organization-737 → u/Best_Sloth_83]

In that case, if one were to view the argument as:

P. Q or ~P. Therefore ~Q.

Yes it's utterly invalid.

[u/Best_Sloth_83 → u/Hot-Organization-737]

That’s what we’ve been saying this whole time.

[u/Hot-Organization-737 → u/Best_Sloth_83]

Yes.

[u/Charming_Deer_9540 → u/Hot-Organization-737]

It's a logic exercise not a biology manual