This article is from the Atheism FAQ, by mathew firstname.lastname@example.org with numerous contributions by others.
There are two traditional types of logical argument: deductive and
1. A deductive argument is one which provides conclusive proof of its
conclusions. It is either valid or invalid.
A valid deductive argument is defined as one where if the premises
are true, then the conclusion must also be true.
2. An inductive argument is one where the premises provide some
evidence for the truth of the conclusion.
Inductive arguments are not valid or invalid, but we can talk
about whether they are better or worse than other arguments. We
can also discuss how likely their premises are.
There are forms of argument in ordinary language which are neither
deductive nor inductive. However, we'll concentrate on deductive
arguments, as they are often viewed as the most rigorous and
Here is an example of a deductive argument:
* Premise: Every event has a cause
* Premise: The universe has a beginning
* Premise: All beginnings involve an event
* Inference: This implies that the beginning of the universe
involved an event
* Inference: Therefore the beginning of the universe had a cause
* Conclusion: The universe had a cause
Note that the conclusion of one argument might be a premise in another
argument. A proposition can only be a premise or a conclusion of a
particular argument; the terms don't make sense in isolation.