Epistemology or theory of knowledge– branch of philosophy concerned with the nature and scope of knowledge. The term was introduced into English by the Scottish philosopher James Frederick Ferrier (1808–1864). Epistemology asks the questions: "What is knowledge?", "How is knowledge acquired?", and "What do people know?"
Occam's Razor– the principle that "entities must not be multiplied beyond necessity" (entia non sunt multiplicanda praeter necessitatem). The popular interpretation of this principle is that the simplest explanation is usually the correct one. However, this is often confused, as the 'simple' "is really referring to the theory with the fewest new assumptions." 
Induction– kind of reasoning that allows for the possibility that the conclusion is false even where all of the premises are true. The premises of an inductive logical argument indicate some degree of support (inductive probability) for the conclusion but do not entail it; i.e. they do not ensure its truth.
Pragmatism– philosophical movement that includes those who claim that an ideology or proposition is true if it works satisfactorily, that the meaning of a proposition is to be found in the practical consequences of accepting it, and that impractical ideas are to be rejected.
Probability theory– branch of mathematics concerned with analysis of random phenomena. The central objects of probability theory are random variables, stochastic processes, and events: mathematical abstractions of non-deterministic events or measured quantities that may either be single occurrences or evolve over time in an apparently random fashion. If repeated many times the sequence of random events will exhibit certain statistical patterns, which can be studied and predicted.