# Clarifications on 1) Modus Ponens, 2) Modus Tollens, 3) Inductive, 4) Incomplete based on examples

My second lecture on Hypothetico-Deductive methods (based on Popper's falsification theory).

In the class, we were given the following examples. We had to classify which examples belong to 1) Modus Ponens, 2) Modus Tollens, 3) Inductive, 4) Incomplete/ill-formed.

1. If John does not attend the meeting, it's going to be boring. However, John is going to attend to the meeting. Therefore, it's not going to be boring.

[My Attempt] ill-formed.

Hypothesis (H): John does not attend the meeting.

Claim (C): Boring meeting then.

However, H (hypothesis) was assumed to be false, that is, John attends the meeting. Then, there is no way to falsify claim. So, it is ill-formed. Right?

1. If you are depressed, you need therapy. You don't need therapy. So, you are not depressed.

[My Attempt] Modus Tollens?

Hypothesis (H): Depression.

Claim (C): require therapy.

However, C (claim) is false, doesn't require therapy. Then, the hypothesis is falsified. Right, which implies Modus Tollens?

1. If the tap water in your neighbor's house is contaminated, then the tap water in your house is contaminated too. The tap water in your neighbor's house is contaminated. Therefore, the tap water in your house is contaminated.

[My Attempt] Modus Ponens?

Hypothesis (H): neighbor's tap water is contaminated.

Claim (C): tap water in our house is contaminated.

However, H is true. Then, C is true => which implies Modus Ponens?

1. If computer program A is more effective than computer program B, then computer program A should outperform computer program B in at least 80% of the tests. Computer program A does in fact outperform computer program B in 80% of the tests. Therefore, computer program A is more effective than computer program B.

[My Attempt] I was unsure between Modus Ponens and Inductive? What do you think?

• 2 is valid and Yes, it is Modus Tollens. – Mauro ALLEGRANZA Aug 29 '19 at 11:06
• 1 is not valid; it is an example of Denying the antecedent fallacy. – Mauro ALLEGRANZA Aug 29 '19 at 11:07
• 3 is Modus Ponens : correct. – Mauro ALLEGRANZA Aug 29 '19 at 11:08
• 4 is not MP; it is invalid : see Affirming the consequent fallacy. – Mauro ALLEGRANZA Aug 29 '19 at 11:10
• The answers Mauro gave above my comment are correct. However it seems to me your justifications on your answers show you are not sure or just scared to make a mistake. It seems to me you want to know WHY the answers are the answers, which is what you SHOULD desire. Just getting the answers us not enough. Understanding the concepts is way way better than memorizing some data that you feel is useless and you will never use again. In all your getting get understanding. The forms have justified reasons why they are valid or invalid. The WHY is what is important. – Logikal Aug 29 '19 at 14:01