Instinctive is often used to mean “controlled by instincts” when describing a specific behavior (as in “an instinctive reaction”). Instinctual has the more analytical meaning “relating to instinct,” often used by scientists when identifying a process or pattern rather than any specific behavior.

At root, instinctive and instinctual are essentially the same; both mean (1) of or arising from the instinct, or (2) pertaining to the instinct. There is a subtle difference between them in some writing on psychology published in the last century. In these contexts, instinctive describes any unlearned response no matter how basic.