argument The process of reasoning from one claim to another. Giving reasons (premises) in support of a conclusion.

assumption A principle taken for granted, without argument or proof.

begging the question Merely restating as the conclusion of an argument one of its premises. Assuming what you are trying to prove.

claim A sentence which could be seen as true or false. A declarative sentence makes a claim.

contradiction The logical relation of two claims in which the truth of one requires the falsity of the other. Two statements contradict each other if it is not possible for them both to be true at the same time and it is not possible for them to be false at the same time.

conclusion The claim that is supported by the others in an argument.

counter-example An example that contradicts a generalization.

deduction A process of reasoning in which the conclusion follows necessarily from the premises. If the premises are true then the conclusion must be true.

epistemology The study of human knowledge, its nature, its sources, and its justifications. This includes the study of relationship and difference between knowledge and belief.

logic The study of correct reasoning.

metaphysics The study of reality, of what there is and how those things are related to each other.
paradox A self-contradictory conclusion from seemingly acceptable premises.

premises The claims that support the conclusion in an argument. The reasons why we should believe that the conclusion is true.

presupposition A principle that is assumed as a precondition for whatever else one believes. Presuppositions are often not examined while used in an argument.

reasons Justifications, evidence, or some other basis for accepting a claim as true.

reductio ad absurdum A form of argument in which on refutes a statement by showing that it leads to self-contradiction or an otherwise intolerable conclusion.

reflection To think about something, to "put it in perspective".

self-contradictory A contradiction within one and the same statement.

sound A valid argument with true premises.

valid An argument in which the reasoning is correct (in the sense that it is truth-preserving).