Difference between Good and Well. Good is an adjective whereas, Well is an adverb. For example: I have a good pen. It writes well. Look at this example. Here the word, Good described or qualified the noun pen. Hence it is an adjective. Whereas, the word well modified the verb writes and hence, it is an adverb. Similarly, the difference between No and Not. No is an adjective but Not is an adverb. Example: I have no pen . My pen is not working. Here No is describing or qualifying the noun pen, whereas, Not is modifying the verb working.