IB Philosophy 3.1.3 Sources of Knowledge Key Definitions

Deductive reasoning is a form of inference in which the conclusion follows necessarily from the premises. If the premises are true and the reasoning is valid, the conclusion must be true (e.g., "All humans are mortal; Socrates is human; therefore Socrates is mortal").

Inductive reasoning is a form of inference in which the conclusion is supported by the premises but does not follow necessarily from them. Induction generalises from particular observations to broader claims (for example, "every swan I have seen is white, therefore all swans are white"), making it probabilistic rather than certain.

Nyaya is a classical school of Indian philosophy that places logic and rigorous epistemological analysis at the centre of philosophical inquiry, recognising four valid means of knowledge: perception, inference, comparison, and testimony. The Nyaya tradition developed a sophisticated theistic argument contending that the orderly operation of karma and the structure of the universe require an omniscient, eternal God as their ultimate coordinator.

Testimony is the acquisition of knowledge through the reports or statements of other people, making it a fundamentally social source of knowledge distinct from perception, reason, or memory. Philosophers debate whether testimony is a basic source of justification in its own right or whether it depends parasitically on the hearer's prior evidence about the speaker's reliability.