Spontaneous, a.
Etymology: [L. spontaneus, fr. sponte of free will, voluntarily.]
1. Proceding from natural feeling, temperament, or disposition, or from a native internal proneness, readiness, or tendency, without constraint; as, a spontaneous gift or proportion.
2. Proceeding from, or acting by, internal impulse, energy, or natural law, without external force; as, spontaneous motion; spontaneous growth.
3. Produced without being planted, or without human labor; as, a spontaneous growth of wood. Spontaneous combustion, combustion produced in a substance by the evolution of heat through the chemical action of its own elements; as, the spontaneous combustion of waste matter saturated with oil. -- Spontaneous generation. (Biol.) See under Generation.
Syn. -- Voluntary; uncompelled; willing. -- Spontaneous, Voluntary. What is voluntary is the result of a volition, or act of choice; it therefore implies some degree of consideration, and may be the result of mere reason without excited feeling. What is spontaneous springs wholly from feeling, or a sudden impulse which admits of no reflection; as, a spontaneous burst of applause. Hence, the term is also applied to things inanimate when they are produced without the determinate purpose or care of man. "Abstinence which is but voluntary fasting, and . . . exercise which is but voluntary labor." J. Seed. Spontaneous joys, where nature has its play, The soul adopts, and owns their firstborn away. Goldsmith. -- Spon*ta"ne*ous*ly, adv. -- Spon*ta"ne*ous*ness, n.
Shades of meaning
That is spontaneous which is freely done, with no external compulsion and, in human actions, without special premeditation or distinct determination of the will; that is voluntary which is freely done with distinct act of will; that is involuntary which is independent of the will, and perhaps in opposition to it; a willing act is not only in accordance with will, but with desire. Thus voluntary and involuntary, which are antonyms of each other, are both partial synonyms of spontaneous. We speak of spontaneous generation, spontaneous combustion, spontaneous sympathy, an involuntary start, an unbidden tear, voluntary agreement, willing submission. A babe's smile in answer to that of its mother is spontaneous; the smile of a pouting child wheedled into good humor is involuntary. In physiology the action of the heart and lungs is called involuntary; the growth of the hair and nails is spontaneous; the action of swallowing is voluntary up to a certain point, beyond which it becomes involuntary or automatic. In the fullest sense of that which is not only without the will but distinctly in opposition to it, or compulsory, involuntary becomes an antonym, not only of voluntary but of spontaneous; as, involuntary servitude. A spontaneous outburst of applause is of necessity an act of volition, but so completely dependent on sympathetic impulse that it would seem frigid to call it voluntary, while to call it involuntary would imply some previous purpose or inclination not to applaud.