An argument is a set of statements consisting of premises and a conclusion. Logic is a branch of philosophy concerned with the relations between premises and conclusions. Part of logic’s task is to establish rules or guidelines about which conclusions can be inferred from a given set of premises.

Consider the following argument:
Any student at UWO who has taken a philosophy course is skilled at reasoning. Jones is a student at UWO. Jones has taken a philosophy course. Therefore, Jones is skilled at reasoning.

We can put this argument schematically as follows:
1. Any student at UWO who has taken a philosophy course is skilled at reasoning.
2. Jones is a student at UWO.
3. Jones has taken a philosophy course.
–––––––––––––––––––––
4. Therefore, Jones is skilled at reasoning.

1. - 3. are the premises of the argument. 4. is the conclusion. 1. - 4. is an argument.

There are two kinds of arguments: deductive and inductive.

Deductive Arguments
An argument is valid (deductively correct) if and only if:
––it is impossible, supposing all the premises are true, for the conclusion to be false.
that is,
––if the premises were to be true, the conclusion would have to be true.
that is,
––the truth of the premises would guarantee (logically, necessarily) the truth of the conclusion.

An argument is sound if and only if:
i) it is valid
and
ii) its premises are true.

Ideally, we want all our arguments to be sound.
Question: Is the argument above (about Jones) valid? sound?

Inductive Arguments
All inductive arguments are invalid, but we still want to be able to distinguish between good and bad inductive arguments.

An inductive argument is an argument in which one infers that as yet unobserved instances of a given kind of thing or event will resemble instances of that kind of thing or event that one has observed in the past. Two kinds:

––a general induction is an inductive argument whose conclusion concerns an entire class.
––a single-case induction is an inductive argument whose conclusion concerns a single instance of some class.

An argument from analogy is an argument in which one uses something one is familiar with to explain something with which one is not familiar.

An argument by inference to the best explanation is an argument in which the premises are true, and they support the conclusion because if the conclusion were true, that would give us the best available reason to expect that the premises would be true.