What kind of fallacy is "that engineering major cheated on his exam. everyone in that department is corrupt!"

 

The statement is a fallacy of composition. It is a fallacy which states that the whole is assumed to have the same properties as its parts. If a part of the whole, which in this case is an engineering major, cheated on the exam, then the whole department must be corrupt. The Fallacy of Composition involves taking attributes of part of an object or class and applying them to the entire object or class.

Step-by-step explanation

Another example of the fallacy of composition are:

1. Because each member of this baseball team is the best in the league for their position, then the team itself must also be the best in the league.
2. Paul is the smartest student in our school. Since he is in my class, I must be in the smartest class.
3. Some people can become millionaires with the right business concept. Therefore, if everyone has the right business concept, everyone will become a millionaire.