They are very close in meaning, I know, but I want to know if there are any subtle differences. Let me give you an example of a subtle difference in meaning between synonyms:
Deceitful vs. deceptive
At first glance, these seem to be perfect synonyms. However, in putting them into sentences, one finds a pattern - deceitful is almost always used of persons, and deceptive is always used of situations or things. So the "perfect" synonyms cannot always replace each other.
My question is: is there a similar subtle difference between continuous and continual?