I too have searched for a definitive answer to this question and not found one. My own way of differentiating grammar from usage errors for my English language learners is as follows:
- If the mistake contravenes a generalizable rule for all members of that word class, then it is a grammar mistake. Otherwise it is a usage mistake.
For example:
He live in Frankfurt contravenes the rule that verbs in the 3rd person singular present simple tense require an -s (with the exception of modals), and is hence a grammar mistake.
My grandfather is a very high man is a usage mistake. We can formulate a rule that high applies to mountains not people. But the rule applies to one member of the word class only and hence the mistake is one of usage.
On this basis, these errors are grammar errors:
- I play tennis yesterday.
- Do you have dog?
- I live in Frankfurt since 10 year. (3 errors)
And these are usage errors:
- I always enjoy to sleep late on Sundays.
- What is the reason of your lateness?
- She replied she didn't know the answer.
The issue is of more than purely theoretical importance because learners need to know whether they should consult a grammar book or a good dictionary/usage manual to find out if what they have written is correct.
It is interesting to note that two excellent resources for English language learners both have the word usage in their titles:
Garner's Modern American Usage and Swan's Practical English Usage.
Garner's book exclusively contains what I personally would define as usage issues, while Swan's includes numerous entries on what I would term grammar; including negation, passive, modals, determiners, etc. So it seems that even the experts can't agree on the meaning of the word.
Profligate has a semantic center of gravity that leans more towards general licentiousness and moral degeneracy, whereas Prodigal is more tightly focused, pertaining specifically to extravagance and wastefulness.
You could validly use profligate as an alternative to prodigal, but there are many times when prodigal would not be appropriate to use in place of profligate.
Best Answer
Distinct means clear, so distinctive means having the quality of clarity, easily recognised for what it is.
To distinguish means to tell apart, to identify. A distinguishing mark heps one to discriminate between two individuals of similar type.
The insignia of a car might be distinctive and easily recognised, but it is the number plates that are the distinguishing marks.