Is slow an adjective and slowly an adverb? — Maryam, Iran
Usually slow is used as an adjective and slowly is used as an adverb, but slow can also be used as an adverb. When an adverb does not have the usual -ly ending it is called a flat adverb or plain adverb and it looks the same as its adjective form.
English teachers will tell you to use slow as an adjective and add -ly when making it an adverb, but in casual speech, informal writing (such as text messages or e-mails to a friend), and even some formal writing slow is often used as an adverb. (Note: Slowly is never used as an adjective.)
Not all flat adverbs have an -ly form (for example, soon is both an adjective and an adverb, and soonly is not a word), but when they do have an -ly form, that is what is preferred by English teachers in formal writing. Below are some example sentences showing how slow and slowly are used.
Slow as an Adjective:
Snails are slow movers.
Learning a new language can be a slow process.
He had a slow horse that never won a race.
They took a slow walk through the park.
Slow and Slowly as Adverbs:
The cars on the road are all moving slow/slowly.
She stood up slow/slowly after falling off her bike.
Her son ate so slow/slowly that it was bedtime when he was finally finished.
The computer was running so slow/slowly that he didn't finish his homework on time.
Notice that in the above sentences, the adverb comes after the verb. Slow and slowly are usually interchangeable when they come after the verb. However, when the adverb comes before the verb, it only sounds natural to use slowly. Below are some example sentences showing this. In each one, slow would never be used.