Healthy vs. HealthfulHow to use "healthy" and "healthful" correctly
Healthy is traditionally used to describe one’s state of health:
Healthful is used to describe something that promotes good health, and even today it should not be used to describe one’s state of health:
healthful children healthful teeth
The second example above, “healthy diet,” is acceptable in contemporary usage but considered incorrect by some traditionalists, who feel that healthy should not be used as a synonym for healthful.
Common Errors in English Usage: Errors in diction and idiom commonly made by native speakers of English
List of Common Errors in English Usage (PDF): Printable version of the complete list
Common Grammar Errors: A list of common errors in grammar (topics like subject-verb agreement and parallelism) as distinct from usage