I saw a phrase saying “protruding eye”. Shouldn’t it be “protruded” ? I couldn’t understand why -ing is used instead of -ed and how the -ing form is used as an adjective here.
protruding itself is an adjective and it means sticking out or projecting.
Therefore it is correct to say protruding eyes
Many adjectives are ing, though there are also ones with ed or the irregular past participle. The meanings can change, too.
- protruding eye [like lizards, a regular type of eye for a lizard]
- protruded eye would be a regular eye that had damage done to it. A forensic analysis by have a term like that in it after a crime or accident.
- broken record [as in for music]; you sound like a broken record (repetitive); one that has been broken.
- breaking news: news that is emerging in the present time. Broken news is not a term.
- flying aces: pilots from WWI.
- flown routes: routes that have been flown by a pilot.
When the ing form is used, it is just a regular adjective. When the past participle is used, it often means something was done to the object.
- moving vehicles, vehicles in motion, that are moving
moved vehicles, vehicles that have been moved
floating beacons, ones that float
- floated beacons, ones that were put in the water and floated
You can often take the verb and analyze it as: an x that [verb] versus an x that has been [verb,past participle].
Often that helps to make the meaning clear.
Protrude is a verb.
Some verbs with the added suffix -ing act as adjectives. Protruding here is defining the characteristic of eyes.
Similar adjectives are "Interesting" ,"Exciting"
-ed is also used to turn verbs into adjectives. For example "Excited" and "Exciting" both are adjectives with different suffix