Infinite vs Infinity: What’s the Difference?

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Infinite vs infinity trips people up because the two words share a root and describe nearly the same idea. The difference is grammar: infinite describes something, while infinity names something. Once you spot the part of speech, choosing the right word gets much easier.

What does infinite mean?

Infinite is an adjective that means having no end, limit or boundary. It describes nouns, so it usually sits right before the thing it modifies or after a linking verb like “is” or “are.”

In everyday speech, people also use infinite to mean extremely great, as in “infinite patience” or “infinite care.” In math and science, it has a stricter meaning: an infinite set, for example, has no final element. The opposite of infinite is finite, and both are adjectives.

Both infinite and infinity trace back to the Latin word infinitus, which means unbounded. It joins in- (not) with finitus (limited).

What does infinity mean?

Infinity is a noun for the quality of being endless, or for a point, distance or quantity beyond any limit. It names the idea itself rather than describing something.

You will often see it after a preposition (“to infinity,” “toward infinity”) or as the subject or object of a sentence (“Infinity is hard to picture”). In math, the symbol ∞ stands for it, and mathematician John Wallis is usually credited with introducing that symbol in the 1600s. Photographers use the word too: a lens can focus “at infinity,” meaning on very distant objects.

Infinity can also modify another noun in fixed terms such as “infinity pool” and “infinity symbol.” In those phrases it is still a noun, working like an adjective.

Infinite vs Infinity: How Do You Use Each One?

Use infinite when you need to describe a noun, and use infinity when you need to name the concept. A quick test: if the word comes before a noun or after “is/are,” you want infinite. If it follows a preposition or acts as the thing being talked about, you want infinity.

• Infinite: “an infinite number of stars,” “the universe is infinite,” “infinite loop.”
• Infinity: “to infinity,” “approaches infinity,” “the concept of infinity.”

You can use both in one sentence: “The list of prime numbers is infinite, so it never reaches infinity; it simply keeps going.” If you need to describe how something is done, the adverb infinitely is the one you want, as in “infinitely more interesting.”

Is Infiniti the same as infinity?

No. Infiniti, spelled with an i at the end, is the name of Nissan’s luxury vehicle brand, which launched in 1989. Infinity, spelled with a y, is the standard English noun.

The brand name is a deliberate respelling, and the capital I is a clue that you are talking about the company. If you are not writing about the car maker, you almost certainly want infinity.

What are the most common infinite vs infinity mistakes?

The most common mistake is using the noun where an adjective is needed, or the other way around. Here are five typical slips:

• ✗ The possibilities are infinity.
  ✓ The possibilities are infinite.
• ✗ The numbers go on to infinite.
  ✓ The numbers go on to infinity.
• ✗ There is an infinity number of stars.
  ✓ There is an infinite number of stars.
• ✗ I’m infinite grateful for your help.
  ✓ I’m infinitely grateful for your help.
• ✗ She just bought a new Infinity sedan.
  ✓ She just bought a new Infiniti sedan.

How can you remember which one to use?

Use a quick swap test or one of these memory tricks to keep the two words straight.

• The swap test: if “endless” fits in the sentence, use infinite. If “endlessness” fits, use infinity.
• Opposites: infinite pairs with finite, and both are adjectives. Infinity ends in “-ty” like city and entity, which are nouns, things you can name.
• The car clue: if you mean the Nissan luxury brand, spell it Infiniti with an i at the end. For everything else, stay with infinity.

Frequently Asked Questions

Is infinite a noun or an adjective?

Infinite is mainly an adjective meaning without end or limit. It can work as a noun in philosophy and theology, as in the Infinite, but in everyday writing treat it as an adjective.

Is infinity an adjective?

No, infinity is a noun. In phrases like infinity pool or infinity symbol it acts as a noun that modifies another noun, which is why those terms use infinity rather than infinite.

Why do we say infinity pool and not infinite pool?

Infinity pool is a fixed term that uses the noun infinity to describe a pool whose edge seems to run on endlessly into the horizon. Infinite pool would suggest a pool that truly has no end.

Is infinity a number?

Not in the ordinary number system. Infinity is a concept of endlessness rather than a real number, though some areas of math use it as a symbol or work with infinite sets and extended number systems.

Is Infiniti the same as infinity?

No. Infiniti is a brand name for Nissan’s luxury cars, while infinity is the standard English noun. Use Infiniti only when you mean the car maker.

Conclusion

The infinite vs infinity question comes down to grammar: infinite describes, infinity names, and Infiniti is a car. Keep the swap test in mind and you will pick the right word every time. Share this with someone who mixes these up, and send them to the quiz at the top.