I was looking for a synonym of spontaneous, and voluntary naturally came to my mind. In an attempt to understand the difference between them, I tried to google spontaneous vs voluntary. To my surprise, nothing really interesting popped up from search results.

Then I decided to look them up respectively. As expected, voluntary is listed as a synonym of spontaneous according to many online resources, and vice versa. However, to my great shock, involuntary is also listed as a synonym of spontaneous by major online dictionaries.

Although the fact does not necessarily imply voluntary and involuntary are synonyms, I continued to look further into voluntary vs involuntary due to confusion.

I found that a voluntary action is something that is done voluntarily or with meaning to do so, while an involuntary action on the other hand is done automatically.

Now I'm even more confused. The word automatically just reminds me of spontaneously, convincing me to believe involuntary is indeed a synonym of spontaneous while voluntary seems less so.

Could someone please justify or explain the contradictions mentioned above? I'm totally lost.

  • @Mari-LouA Thanks for correcting me.
    – Terry Li
    Commented Aug 15, 2015 at 16:06

2 Answers 2


A voluntary action is one that the actor, employing free will, chooses to take.

An involuntary action is one that takes place out of the control of the actor, or against the actor's will.

Spontaneous has several related definitions. A spontaneous action can be one that the actor takes without a significant amount of forethought ("a spontaneous purchase"). In that case, the spontaneous action is voluntary.

On the other hand, spontaneous can also refer to something that occurs with no apparent cause ("spontaneous combustion"). By its nature, this activity rarely involves an overt "actor" per se. When it involves a living organism ("spontaneous growth", "spontaneous motion", etc.), the action is probably involuntary.

Spontaneous has a few other definitions as well. Generally, you'll have to discern the difference from context. When you see the word "spontaneous" used to describe an action taken by a clearly definable actor, though, the action is probably voluntary (although it might not be).

  • I think spontaneous combustion is a good example of spontaneously/involuntary :)
    – Lynn
    Commented Nov 12, 2011 at 1:05

Even though voluntary is the opposite of involuntary, they do have something in common. Consider the following meanings:

  • Voluntary describes an action taken by an actor without being compelled to do so by someone else.
  • Involuntary describes an action performed without the actor's will.
  • Spontaneous is something that happens without intervention of something else.

All three cases involve something which does not interfere with the action.

  • voluntary: EXTERNAL ENTITY does not interfere with ACTOR performing ACTION.
  • involuntary: ACTOR does not interfere with ACTION

So both are spontaneous, but with a different non-interfering part.

  • -1. This is not a good answer. Your definition of spontaneous is a secondary definition of the word that only applies to natural phenomena, and is inapplicable to voluntary or involuntary actions.
    – jprete
    Commented Nov 12, 2011 at 3:04

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