When comparing "spare of the moment" vs "spur of the moment," only one form is correct: spur of the moment. "Spare of the moment" is a mishearing that sounds plausible in fast speech but doesn't exist in any standard dictionary. It's a good example of an eggcorn: a word or phrase swapped for a similarly sounding one that feels logical even though it isn't.
What "spur of the moment" actually means
Spur of the moment describes something done impulsively, without planning. It captures the idea of acting the instant an impulse arrives, before reflection kicks in. You can use it as an adverb phrase ("I booked the flight spur of the moment") or as a hyphenated adjective before a noun ("a spur-of-the-moment decision").
The word "spur" is doing real work here. A spur is a pointed device worn on a rider's boot to urge a horse forward immediately. The image is precise: a sharp, sudden prompt to action. "Spare," by contrast, means surplus or leftover. A "spare of the moment" would suggest something idle or extra, which is the opposite of what the phrase intends.
Why people write "spare of the moment"
The error is almost entirely phonetic. In natural speech, "spur" and "spare" sit close together. Both are single syllables starting with "sp" and ending with an "r" sound. When someone hears the phrase rather than reads it, the brain can latch onto the more familiar word. "Spare" is a common everyday word. "Spur" as a metaphor is less frequently encountered outside equestrian contexts, so the mind fills the gap with what it knows.
This same pattern drives errors like "cease the day" for "seize the day", where the correct but less familiar word gets replaced by something that sounds similar and feels close enough. The mechanism is identical: mishearing followed by plausible-looking reconstruction.
How to use "spur of the moment" correctly
The phrase works in two positions. As an adverb phrase, it follows the verb and needs no hyphens:
- "She decided to go spur of the moment."
- "They left spur of the moment and didn't pack properly."
As a compound adjective modifying a noun, hyphenate it:
"It was a spur-of-the-moment trip." Not "a spur of the moment trip." The hyphens signal that all four words are working together as a single descriptor. Drop them when the phrase comes after the noun it describes.
Is "spare of the moment" ever correct?
No. It doesn't appear in any standard dictionary, and no established idiom uses this construction. If you've written it, replace it with "spur of the moment" every time. There's no context where "spare of the moment" conveys a distinct meaning, unlike pairs such as vicious vs viscous, where both words are real and the choice depends on what you mean.
Quick test before you write it
Ask yourself: is the action sudden, unplanned, driven by a sharp impulse? Then the word is "spur." Think of the boot spur prodding a horse into motion. That image holds the phrase in place. Spare means extra or free. Nothing about impulsive spontaneity involves surplus.
One more thing worth noting: the hyphenated form "spur-of-the-moment" is also sometimes written without hyphens even in the adjective position in informal contexts. Major style guides prefer the hyphens before a noun, but either way, the first word is always "spur."