spon·ta·ne·ous (spn-tn-s) KEY
From Late Latin spontneus, of one's own accord, from Latin sponte; see (s)pen- in Indo-European roots
spontaneous, impulsive, instinctive, involuntary, automatic
These adjectives mean acting, reacting, or happening without apparent forethought or prompting. Spontaneous applies to what arises naturally rather than resulting from external constraint or stimulus: "The highest and best form of efficiency is the spontaneous cooperation of a free people" (Woodrow Wilson). Impulsive refers to the operation of a sudden urge or feeling not governed by reason: Buying a car was an impulsive act that he immediately regretted. Instinctive implies behavior that is a natural consequence of membership in a species. The term also applies to what reflects or comes about as a result of a natural inclination or innate impulse: Helping people in an emergency seems as instinctive as breathing. Involuntary refers to what is not subject to the control of the will: "People drew in their breath with involuntary surprise and suspense" (Harriet Beecher Stowe). Automatic implies an unvarying mechanical response or reaction: She accepted the subpoena with an automatic "thank you."