Spontaneous

 An “I’m feeling spontaneous” T-shirt (Ѻ); showing the thermodynamics behind the phrase, namely a change that involves a free energy decrease.
In science, spontaneous, a 1656 term, meaning “occurring without external stimulus”, from the Latin sponte “of one’s own accord, willingly”; something that proceeds from natural feeling or native tendency without external constraint; arises from momentary impulse; controlled or directed internally; developed without apparent external influence, force, or cause, or treatment; not apparently contrived or manipulated: natural. [1]

Etymology
The term “spontaneous combustion” was used in 1795. [2]

In 1891, English thermodynamicist John Parker (c.1860-c.1930), a St. John’s College, Cambridge, seventh wrangler (1882) and fellow (1889) (Ѻ), in his Elementary Thermodynamics, in his thermodynamic potential chapter, was citing Willard Gibbs (1876) and Hermann Helmholtz (1882), and employing the term spontaneous as follows, modern notation translation (see: characteristic function notation table) shown below: [3]

“When the only external forces to which the body is subjected consist of a uniform and constant normal pressure, P, on the surface, dW = – PdV, so that if we write G for H + PV, or U – TS + PV, the preceding result becomes:

$dG = 0 \,$

If, under these conditions, V be also constant, then:

$dH=0\,$

Let us now suppose that the system is in equilibrium in any state A at any uniform temperature T. Then the equilibrium in the state A will be unstable if a slight shake or touch, by which no perceptible change is made in the system, causes the equilibrium to be broken in consequence of which the system rushes into some other state P. Hence clearly the equilibrium in the state A will be stable if every spontaneous change of state, like AP, is impossible.”

Love | Spontaneity
The is, for some, a strong sense of spontaneity and or a spontaneousness associated with the actions or process of love, falling in love (see also: fall-force), and or love at first sight. American philosopher Robert Solomon gives his somewhat ambiguous take on the situation as follows: [5]

“We often contrast the ‘spontaneity’ of the passions with the ‘ponderous deliberations’ of reason. And it is true that we often ‘find ourselves’ in a passion. But this appearance must be explained. The fact that we ‘find’ this to be the case does not entail nor even suggest that we are not ourselves responsible for them. And we all know so well that many times we ‘catch ourselves’, not in a passion, but deliberating—even ponderously—in an effort to build up a passion, ‘working ourselves into a rage’, ‘making ourselves feel guilty’, or rehearsing the virtues and possibilities of a prospective ‘date’ until we virtually push ourselves into the dubious abyss into which we allegedly ‘fall’ when we ‘fall in love’. There is nothing ‘spontaneous’ about such emotion. And even when our passions are unquestionably spontaneous in that sense, it remains to be seen whether they are not so only because they have been used in similar circumstances so many times before and have already been so often practiced and finely developed. Like the apparently ‘spontaneous’ genius of a Nicolo Paganini, a James Whistler, or a Thomas Mann, our passions are ‘spontaneous’ only in the sense that they can benefit from many years of hard work and painful development; and the present masterpiece seems to emerge as if on its own.”

“The clarification in the idiom "waste not free energy" is the recognition that free energy is something that is released from transformations in relationships, and is a function of both enthalpy and entropy. Hence, if you find yourself in a dead equilibrium level relationship or situation, there is no free energy change, and hence you are wasting your existence, but when you do find spontaneous reactions (e.g. love at first sight), treasure it and make the best use of it.”
Libb Thims (2011), post to Eddie Devere’s blog “Thoughts on the Thermodynamic Imperative” (Ѻ)

Quotes
The following are related quotes:

“I wish to lay special emphasis on the word spontaneous in this title, as embodying my conception of pure sociology. Whatever is spontaneous is pure in this sense. Its two other chief synonyms are ‘genetic’ and ‘natural’ as opposed to ‘telic’ and ‘artificial.’ Still, as the telic faculty is itself a genetic product, it cannot be omitted from a treatment of pure sociology, and, as I have shown, its manifestations are in one sense as strictly spontaneous as are those of the dynamic agent.”
Lester Ward (1903), Pure Sociology: a Treatise on the Origin and Spontaneous Development of Society [4]

 ● Floating magnets experiment● Spontaneity● Spontaneity criterion● Spontaneity table ● Spontaneous process● Spontaneous reaction● Spontaneous combustion

References
1. (a) Merriam-Webster Collegiate Dictionary, 2000.
(b) Spontaneous – Online Etymology Dictionary.
2. Spontaneous – Online Etymology Dictionary.
3. Parker, John. (1891). Elementary Thermodynamics (§10: Thermodynamic Potential, pgs. 325-43; spontaneous, pgs. 328-30). Cambridge University Press.
4. Ward, Lester F. (1903). Pure Sociology: a Treatise on the Origin and Spontaneous Development of Society (thermodynamics, pgs. 97, 168). MacMillan, 1907.
5. Solomon, Robert C. (1993). The Passions: Emotions and the Meaning of Life (pg. 60). Hackett Publishing.