Adjectives as Verbs in English — how adjectives become verbs, clear rules, tests and examples

Short overview

There are two related facts people often confuse:

• Adjectives can appear after linking verbs (be, seem, look). That doesn’t make them verbs — they are still adjectives: e.g. "The door is closed." (closed = adjective)
• Some adjectives can be used as verbs, either by simple conversion (zero-derivation) or by adding a suffix (like -en, -ify, -ize): e.g. "Please close the door." (close = verb)

How to tell whether a word is acting as an adjective or as a verb

Use these quick tests. If the word behaves like these, it is a verb; if it behaves like these, it is an adjective.

• Object test: Verbs can take objects: "Please empty the box." Adjectives cannot: *"Please empty the box is big." (incorrect)
• Progressive (‑ing) test: Verbs can form progressive: "He is emptying the bottle." Adjectives cannot usually be used this way: "He is empty the bottle." (wrong) Note: present participles (‑ing) can be adjectives too ("an interesting story").
• Very / degree test: Adjectives accept degree words: "very clean, more beautiful". You cannot sensibly say "very clean the table" when clean is used as a verb.
• Comparative/superlative: Adjectives can take comparatives (cleaner, more beautiful). When the form is clearly a comparative used as a verb agent ("a cleaner"), that’s a noun from the verb.
• Passive/result test: If a form can be followed by a prepositional phrase indicating state after an action, check whether it’s a result-state adjective or a passive verb: "The window was broken" (could be passive verb or adjective—context decides). "The window is broken" is usually an adjective describing state; "Someone broke the window / The window was broken by a ball" is passive verb.

Common ways adjectives become verbs

• Zero-derivation (no change): same form works as adjective and verb
  • clean (adj: "The room is clean." / verb: "Please clean the room.")
  • empty (adj: "The box is empty." / verb: "Empty the box.")
  • warm, cool, dry, slow ("Warm the soup." vs "The soup is warm.")
• Suffixation
  • -en: bright → brighten, short → shorten, wide → widen
  • -ify: simple → simplify, pure → purify
  • -ize/-ise: modern → modernize, legal → legalize
• Participles: verb forms that act like adjectives
  • Present participle as adjective: "an interesting film" (adjective)
  • Past participle as adjective: "The door is locked." (may be adjective or passive verb—context matters)

Examples that show the difference

• clean: "The kitchen is clean." (adjective) vs "Clean the kitchen." (verb)
• empty: "The cup is empty." (adjective) vs "Empty the cup." (verb)
• broken: "The window is broken." (adjective/state) vs "They have broken the window." (verb action) vs "The window was broken by a kid." (passive verb)
• interesting / interest: "The book is interesting." (adjective) vs "The book interests me." (verb)
• bright / brighten: "The room is bright." (adjective) vs "Open the curtains to brighten the room." (verb from adjective + -en)

Summary (step-by-step approach when you’re unsure)

1. Try to add an object. If it works, it’s a verb.
2. Try the progressive (is …ing). If that makes sense, it’s likely a verb.
3. Try using a degree word like "very" or making a comparative. If that works, it’s an adjective.
4. Look for derivational clues: forms with -en, -ify, -ize are verbs made from adjectives.

If you want, give me 5 example sentences and I’ll label each word as adjective or verb and explain why.