The first exercise is "Spot the valid argument(s)." The following are the arguments.

I think all of these arguments are valid. Am I right?


If abortion is permissible, infanticide is permissible.

Infanticide is not permissible.

Therfor, abortion is not permissible.


It is wrong to experiment on a human subject without consent.

Dr. X experimented on Mr.Z.

Mr.Z consented to this experiment.

Therefore, it was not wrong for Dr.X to experiment on Mr.Z.


I will not survive my death.

My body will survive my death.

Therefore, I am not my body.


Geoffrey is a giraffe.

If X is a giraffe, then X's parents were giraffes.

Therefore, all of Geoffrey's ancestors were giraffes.

The second exercise is "The following arguments are not valid as they stand. Supply missing premises to make them valid."

I could not understand why the first argument is invalid. Is it because "the universe" is a member of "every event," and so the premise is TRUE and the conclusion is FALSE?

Besides, how could I make this argument valid by adding premises?


Every event has a cause.

No event causes itself.

Therefore, the universe has no beginning in time.

The philosophical rhetoric of logic may not be acceptable on MSE, but I'll do my best to stay mathematical here.

For the first part, I've got my doubts about (ii). Non-consent is one thing that could make a human experiment wrong, but it is not necessarily the only thing. For instance, if it is wrong to experiment on a human subject when the appropriate animal testing hasn't been completed, then Mr. Z's consent by itself would not be sufficient to justify the conclusion.

For the second part, it seems to me that the conclusion is talking about time when none of the premises do, so there's certainly a disconnect there. At a minimum, you'd need to assume that every event is preceded by its cause, but more yet may be required.


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