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.