Some words have an -al on the end. Some don't. Some can do either. Here are those words.
| Without -al | With -al | Mean the same? |
|---|---|---|
| analytic | analytical | not really |
| symbolic | symbolical | yes? |
| scientific | scientifical | yes; the latter exists but is obsolete |
| theoretic | theoretical | where both are acceptable, yes ("set-theoretic" vs "set-theoretical"), but the latter is more widely acceptable |
| geometric | geometrical | yes |
| acoustic | acoustical | uses of the latter are a subset of uses of the former |
See also the superb answers to the question Why is it geometric but theoretical?