**Category:**

**Definition:** Any argument of the form: If A then B, B, therefore A

**Examples:**

- If I am in Calgary, then I am in Alberta. I am in Alberta. Therefore, I am in Calgary. (Of course, even though the premisses are true, I might be in Edmonton, Alberta.) ,
- If the mill were polluting the river then we would see an increase in fish deaths. And fish deaths have increased. Thus, the mill is polluting the river.

**Proof:**

Any argument of the following form is invalid:
If A happens then B will happen (First premiss)
B happened (Second premiss)
Therefore, A happened (Conclusion)

Show that even though the premises are true, the conclusion could be false. In general, show that B might be a consequence of something other than A. For example, the fish deaths might be caused by pesticide run-off, and not the mill. (Barker: 69, Cedarblom and Paulsen: 24, Copi and Cohen: 241)

Created by Stephen Downes, Copyright 2023 CC By-NC-SA