Here is an invalid argument that I came across at DCT&P several years ago:
Apples are spherical.
Balls are spherical.
An apple is a ball.
Can anyone explain what is wrong with this argument?
(The argument might look better with oranges instead of apples since they are more spherical, but that has nothing to do with what's wrong with it.)
Here is a web site that can help you learn to recognize logical fallacies in categorical syllogisms: