Gradable and non-gradable

I'd like to know how to discover when a adjective or adverb is gradable or non-gradable, without having to know a large list by heart. Can anybody help me?
Thanks.

I don't understand the question. Do you mean gradable as in degrees -- "pretty, prettier, prettiest"? Or non-gradable meaning an absolute --"unique"? Something is unique or it's not.

Here's what I found:

"Adjectives can be divided into gradable and non-gradable (or classifying) adjectives. Gradable adjectives can be compared (happy-happier-happiest, good-better-best, beautiful-more beautiful-most beautiful) and modified with the intensifying word very. Non-gradable adjectives do not have comparative or superlative forms nor are they intensified: a financial plan, an electric train, semantic criteria." www.helsinki.fi/~mpalande/adjectives.html

Another good site is:
www.grammarstation.com/ SpelltheAdjectives.html

Look! For an English native the gradability can possibly be considered easy, but not for other origin peoples, for instance the Latins's origin.
To realize how difficult it is, take a glance at the site about gradable and ungradable adjecitves modifiers on the site:www.edict.com.hk/funcgrammar/NonGradable/Participles.htm.
Thanks, HCD