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.

Instinctive behaviors are immediate and automatic reactions to specific stimuli, based on inherited tendencies. On the other hand, instinctual behaviors, while also rooted in biology, imply a deeper, often more complex set of behaviors that are part of an organism's innate programming.

While both terms are often used interchangeably in casual conversation, "instinctually" might be preferred when emphasizing a connection to deeper, more primal instincts tied to survival or fundamental behaviors.