Gradable and Non-gradable Adjectives

Gradable vs. Non-gradable Adjectives 

Gradable Adjectives

The adjectives that describe qualities that can be measured, guessed or compared are called gradable adjectives. Gradable adjectives can have comparative and superlative forms, and they can be modified by adverbs.

For example, the height of an object can be guessed, measured or compared. You can easily say, "The tree is shorter than the building". After some years, you will say, "The tree is now taller than the building". Thus short, tall, etc. are gradable adjectives.

Non-gradable or Strong Adjectives

The adjectives that describe qualities that can be either present or absent but not measured, guessed or compared are called non-gradable or strong adjectives. Non-gradable adjectives cannot have comparative or superlative forms, nor can they be modified by adverbs. 

Exception: With the help of some verbs such as feel, sound, look, etc., some non-gradable adjectives can be used as gradable ones in some cases. 

Let's discuss the adjective 'dead'. It means the absence of life. That cow is dead- means there is no life in that cow. Can you say "That cow is more dead"? or "less dead"? Once the cow's heart stopped beating, it has become dead. There cannot be any degree of being dead. Well, the cow may be sick before it is dead, but that's another adjective.
Here comes the exception. Suppose you are not sure if a cow is dead. Perhaps two injured cows are lying still on the road. Now your friend might say,  "The white cow looks more dead than the black one". It means your friend thinks the possibility of the white cow being dead is more than the black one. Such sentences are possible although the adjective 'dead' is Non-gradable. The reason is that look/seem doesn't mean a confirmed state.

Non-gradable adjectives can be classified into three categories:

Absolute: Alive Correct Dead Impossible Unique
Extreme: Excellent Freezing Gigantic Enormous Furious

Classifying: Chemical Digital Domestic Environmental

Intensifiers for Non-gradable or Strong Adjectives 

You may use these intensifiers with non-gradable or strong adjectives: absolutely, completely, exceptionally, particularly, really, quite, totally, utterly

Never use 'very' with non-gradable or strong adjectivcs.