1. Good & Well

GOOD is an adjective but WELL is both an adjective and adverb.

A) We use GOOD for people/things to say that they are very satisfactory, enjoyable,  pleasant, interesting, morally right, kind, helpful, able to do well or successful, whereas we use WELL as an adjective to tell one’s health condition; e.g.

i) Climate of this place is really good.
ii) My wife is very good with children
iii) He is not very well today.
iv) When she came home from school she really didn’t look well.

B)  WELL can be used as an adverb also. We use WELL to say that something is done to a high standard or to a great extent. We can’t use GOOD as an adverb; e.g.

INCORRECT: He speaks English good.
CORRECT: He speaks English well.

C) GOOD = large

Used to emphasize the large number, amount, or level of something; e.g.

i) I’ve run a good distance today.
ii) There is a good-sized crowd waiting for the minister.

2. Bad & Ill

BAD is an adjective but ILL is both an adjective and adverb.

A) We use BAD for people/things to say that they are unpleasant and causing difficulties or harm, of low quality, not acceptable, whereas we use ILL as an adjective to tell one’s health condition. ILL (=sick) is usually used after a verb, before a noun use SICK; e.g.

i) I could not leave home because of bad weather.
ii) My father had a very bad night last night. (= did not sleep well)
iii) He’s been ill with dengue.
iv) My father is a very sick man.

INCORRECT: She is well trained to look after ill children.
CORRECT: She is well trained to look after sick children.

NOTE-I: Normally we don’t use ILL before a noun, but we can do so when we are also using an adverb such as seriously, chronically, or terminally; e.g.

That ward is for chronically ill patients.

NOTE-II: We don’t use ILL or SICK to say that someone has received an injury. Say that they are injured or hurt; e.g.

INCORRECT: He was ill and taken to hospital after the accident.
CORRECT: He was injured and taken to hospital after the accident.

B) ILL can be used as an adverb also. ILL as an adverb means Badly, Imperfect, Unfavourably; e.g.

i) He treated me really ill.
ii) They were ill provided with weapons. (here ILL = insufficiently)

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