Assignment 3.2: Assessing logical validity

Purpose of the assignment

You will practice distinguishing logical validity from logical invalidity.

Subject matter

Section 3.3

Tasks

For each of the following examples, decide

  • which of the four classical reasoning schemes is used;
  • whether the arguments are correct;
  • whether the conclusion is correct;
  • whether the reasoning is valid or invalid.

Reasoning A

People are mortal.

Dogs are not people.

Conclusion: dogs are not mortal.

Reasoning B 

In all American cities there are skyscrapers.

Toronto is an American city.

Conclusion: there are skyscrapers in Toronto.

Reasoning C 

All countries that have the euro as their currency are in Europe.

Denmark is not in Europe.

Conclusion: Denmark does not have the euro as its currency.