The phrase "a spontaneous act" is correct and usable in written English.
It can be used to describe an action that is done impulsively or without premeditation.
Example: "Her decision to travel to Paris on a whim was truly a spontaneous act that surprised everyone."
Alternatives: "an impulsive action" or "a sudden decision".
It's not just a spontaneous act for me.
Their entire argument was a spontaneous act of theater performed for the benefit of other passengers.
Security experts said the fact that two handguns had been used suggested premeditation, as opposed to a spontaneous act.
Marketing staff are free to carry out a spontaneous act of kindness at any given moment, she adds.
So often in life, someone remembers a spontaneous act of kindness from a total stranger, and in turn, passes on an act of kindness to others.
Ripping out the kitchen sink is not a spontaneous act; the money has already been put aside even if it has not yet been spent.
Rajeev Masand noted: "Farhan Akhtar delivers a simple-enough likeable performance that is just what the film required — no showy flourishes, no loud outbursts, just a straight off spontaneous act that works like a dream".
Dancing became a naughty and spontaneous act for the drunken and daring, performed atop cocktail tables and on banquettes.
Moreover, the vehemence and brutality of Hazel's assault, Elizabeth came to feel, belied a random and spontaneous act.
It was, as Jia Tolentino wrote recently, a more or less spontaneous act of reaffirmation, a chance for people who feel repudiated by their fellow-citizens to get together and remind themselves that they aren't alone — in fact, they are the majority.
Believe it or not, this isn't the first Ingress story I've heard that involves crowd-funded air travel – the other involves a sea-plane, a remote Scandinavian island and spontaneous act of sabotage.
