The Oxford English Dictionary (second edition, 1989) devotes a remarkable 7 and 9 pages, respectively, to good and well (in a mixture of 7- and 9-point type). Good and well are not synonyms, but their myriad meanings, interpretations, combinations, and usages are often similar, and thus each has the potential to be used incorrectly, if inadvertently. This post addresses good and well when describing the state of being of something or someone.
In this context, good is an adjective (modifies only nouns):
The researcher has a good idea [modifies a noun].
Her idea is good [modifies a noun and uses a linking verb that expresses a state of being, eg, to be, to seem, to appear].
Well is an adverb (can modify verbs, adjectives, or other adverbs). As an adjective, well can also be used as an adjective to mean “in good health.”
The patient did well [scored well, performed well] on the Mini-Mental State Examination.
The patient spoke well of her physician.
The patient articulated her concerns well.
The patient does not feel well.
Well may also be used to mean good health in its combined form: a well-baby checkup.
But: A usage note in Webster’s1 points out that “An old notion that it is wrong to say ‘I feel good’ in reference to health still occas. [occasionally] appears in print. The origins of this notion are obscure, but they seem to combine someone’s idea that good should be reserved to describe virtue and uncertainty about whether an adverb or an adjective should follow feel. Today nearly everyone agrees that both good and well can be predicate adjectives after feel. Both are used to express good health, but good may connote good spirits in addition to good health.” Moreover, Webster’s reports, “Adverbial good is primarily a spoken form; in writing it occurs in reported and fictional speech and in generally familiar or informal contexts.”
As a general rule of thumb: Things are good. One does things well.
Be well. And be good. —Roxanne K. Young, ELS
1. Merriam-Webster’s Collegiate Dictionary. 11th ed. Springfield, MA: Merriam-Webster; 2003.