Before understanding the difference between the two, let’s first look at the four criteria for being an adjective.
- It can occur in attributive position.
- It can occur in predicative position.
- It can be pre-modified by very.
- It shows comparative and superlative forms.
The first two criteria are the core to being an adjective. A word that misses both is not an adjective. A word that meets one is peripheral adjective. A word that meets both is central adjective. To put it differently, a central adjective will fulfil at least the first two criteria, and a peripheral adjective will fulfil at least one of the first two criteria.
You can say that central adjectives are more adjectival than peripheral adjectives, just like chimpanzees are more human than gorillas (based on percent DNA match with humans).
Here are few examples of central and peripheral adjectives:
Examples of central adjectives
The first in each set is an example of attributive use; the second of predicative use.
1A. She wore a happy smile.
1B. He seems happy with the results.
2A. The busy street was filled with cars.
2B. The manager is always busy during meetings.
3A. I wore a cold expression to hide my feelings.
3B. The water feels cold today.
4A. The tired employees went home early.
4B. She looks tired after the long trip.
Examples of peripheral adjectives
These adjectives function only attributively.
1. The main issue is finding a solution that works for everyone. [Predicative use, The issue is main, makes no sense.]
2. His elder sister lives in London.
3. The indoor pool is heated throughout the winter.
4. The former president gave a speech at the conference.
These adjectives function only predicatively.
5. Martha is aware of the risks involved. [Attributive use, aware Martha, makes no sense.]
6. I’m glad you could join us for dinner.
7. He is afraid of flying in airplanes.
8. She’s not averse to trying new things.
Few resources on grammar mention that an adjective should fulfil all four criteria to be termed central. Otherwise, it’ll be peripheral. So, as per them, dead and impossible are peripheral since they fulfil only the first two criteria.
However, many resources don’t consider third and fourth criteria as essential to being an adjective. (That’s what has been followed in this post.) That’s because adverbs too fulfil these two. For example, quickly can be modified by very (very quickly), and it shows comparative and superlative forms (more quickly and most quickly).
As per these resources, dead and impossible are central adjectives.
