Inductive reasoning presupposes

Concept — An inductive argument moves from a limited number of observed particular cases to a general conclusion that also covers cases nobody has examined. That step is not deductively guaranteed by the premises, so induction always leans on a standing background assumption: that the subject matter is regular, so that unexamined instances follow the same pattern as the examined ones. In logic and philosophy of science this background assumption is named the principle of the uniformity of nature.

Application — The subject matter of this question is human nature. An inductive claim about people — say, that people who are rewarded for a behaviour tend to repeat it — is drawn from a sample of individuals and then extended to human beings in general. That extension is licensed only if human nature repeats itself from one case to the next, so the background regularity assumption stated above has to be read here as a claim about human nature itself.

Contrast — The other three notions are claims of a different kind, and none of them supplies the regularity an inductive leap needs:

• unity in human nature — the metaphysical claim that humankind forms one indivisible whole; oneness of the species does not by itself entail that a trait recurs identically from person to person.

• integrity in human nature — the ethical claim of moral wholeness, consistency between professed principle and actual conduct; it evaluates character instead of describing how cases repeat.

• harmony in human nature — the claim that human faculties, or human beings, adjust agreeably to one another; agreement of this sort is compatible with wide variation between individual cases.

Cross-check — Withdraw the uniformity assumption and every inductive generalisation collapses at once: if human nature were free to differ arbitrarily in the very next unexamined case, no sample could tell us anything about the rest. Hume's problem of induction is exactly the difficulty of justifying this assumption — which confirms that uniformity is something induction takes for granted at the start, not something it proves at the end.

Result — Inductive reasoning presupposes uniformity in human nature.