Why do some words have suffixes -ic and -ical and how are they different?

Question

At the moment I am thinking of the word historic vs. historical. Fantastic and fantastical are another set.

When is it appropriate to use each word, and why doesn't the suffix -ical exist with words like epic and dramatic?

Answer 1

The OED distinguishes the two forms in a broad manner:

Many adjectives have a form both in -ic and -ical, and in such cases that in -ical is usually the earlier and that more used. Often also the form in -ic is restricted to the sense ‘of’ or ‘of the nature of’ the subject in question, while that in -ical has wider or more transferred senses, including that of ‘practically connected’ or ‘dealing with’ the subject. Cf. ‘economic science’, ‘an economical wife’, ‘prophetic words’, ‘prophetical studies’, ‘a comic song’, ‘a comical incident’, ‘the tragic muse’, ‘his tragical fate’. A historic book is one mentioned or famous in history, a historical treatise contains or deals with history. But in many cases this distinction is, from the nature of the subject, difficult to maintain, or entirely inappreciable.