Is there a rule about when an adjective should end with "ic" or "ical"?


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    meta, "The Cambridge Guide to English Usage" has an entry named "-ic/-ical" in which it is said "Is there any reason for preferring one over the other? Often the answer is no." What does "Often" mean there? "Often" means that you should consult a dictionary each time you have to use an ic/ical adjective! – user114 Jul 16 '13 at 21:28
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    ... in fact in certain cases there is a great divergence in meaning, like it happen to econimic/al, historic/al and politic/al, but, fortunately, apart kinetic/al, the other adjectives you cited don't have this problem. – user114 Jul 16 '13 at 21:36
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    There's some very useful information in this answer to a similar question on ELU, but the bottom line, as @Carlo says, is that you probably ought to consult a dictionary fairly often (but if you don't have any reference tools to hand and you have to make a choice on the fly, you'll get it right more often than not if you always go for -ic). – FumbleFingers Jul 16 '13 at 21:37

The NOAD says that the -ical suffix is used to form adjectives:

  • Corresponding to nouns or adjectives usually ending in -ic (such as comical corresponding to comic)
  • Corresponding to nouns ending in -y (such as pathological corresponding to pathology)

As for the words you list, the NOAD says:

  • Geometric and geometrical are both adjectives, with the latter being a derivative of the first
  • Analytic is another term for analytical
  • Theoretic is another term for theoretical
  • Kinetical is not a word listed by the NOAD

In some cases, a suffix is preferred over the other one, but there isn't a rule that explains in every case when to use one or the other.

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