Not Every Adverb Ends in -ly, and Some -ly Words Are Adjectives
Most people learn that adverbs end in -ly. It is a useful starting point and it produces two persistent errors.
Flat adverbs: no -ly needed
Some words serve as both adjective and adverb without changing form. These are called flat adverbs:
- fast — a fast car / she drove fast
- hard — hard work / she worked hard
- late — a late train / it arrived late
- early, straight, right, wrong, far, near, deep, high, low
There is no such word as fastly. She drove fast is not casual speech — it is the only correct form.
The ones with two forms and two meanings
A handful have both a flat form and an -ly form that mean different things. These are worth knowing individually:
- hard (with effort) / hardly (barely). She worked hard against she hardly worked — opposite meanings.
- late (not on time) / lately (recently).
- near (close) / nearly (almost).
- deep (physically) / deeply (emotionally). Dig deep against deeply moved.
- high (physically) / highly (very). Fly high against highly regarded.
- free (without cost) / freely (without restriction). Eat free against speak freely.
Hard and hardly is the one that causes real confusion, because the meanings are opposites rather than shades.
-ly words that are adjectives
The reverse trap. These end in -ly and describe nouns, not verbs:
- friendly, lonely, lively, lovely, silly, ugly, likely, deadly, elderly, cowardly, orderly
English has no adverb form for most of these — friendlily is technically possible and nobody says it. You have to rewrite: she greeted him in a friendly way.
This matters for hyphenation. The rule that compound adjectives skip the hyphen after an -ly adverb does not apply here, because these are not adverbs: a family-run business, an early-morning train both keep their hyphens.
The famous one
Think different. Go slow. Drive safe.
Frequently called errors. Slow is a legitimate flat adverb with centuries of use, so go slow is defensible. Safe and different are not established flat adverbs, so those are genuinely non-standard — used deliberately, in both cases, for rhythm.
Which is a reasonable thing for a slogan to do and a poor model for a report.
The test that actually works
Forget the ending. Ask what the word is describing.
Describing a noun, it is an adjective, whatever it ends in. Describing a verb, an adjective or another adverb, it is an adverb, whatever it ends in.
Checked against Merriam-Webster, the Chicago Manual of Style and the AP Stylebook. Spotted an error? Tell us — see our editorial policy.
