Is there a rule about when an adjective should end with “ic” or “ical”?
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.
Source : Link , Question Author : user5402 , Answer Author : apaderno