There are many adjectives (describing words) that are formed from nouns using the suffixes –ic or –ical. Sometimes a noun can be transformed into both adjectives.
Economy, economic, economical
History, historic, historical
Class, classic, classical
How do you know which of the two adjectives to use?
According to Peter’s Pragmatic Guide to Idiomatic English: http://www.unil.ch/webdav/site/angl/shared/pdf/Resources/PPG14thed.pdf
“Consider the first (–ic) as the ‘true’ or ‘direct’ form, and the second
(–ical) as only indirectly related to the concept in question.”
It was Obama’s economic policy that dictated her choice of an economical car.
“Here economic relates to money; economical relates first of all to petrol consumption,and thus only indirectly to economics,” Peter explains.
A classic is something that is taught or cited in class, such as classic physics, whereas classical literature, art and music are from a previous era.
A historic event is one that made history. A historical novel is one with a setting that occurred in the past.
Sometimes a noun ends with –ic, so the related adjective ends with –ical.
Skeptic, skeptical (Brit-speak: sceptic, sceptical)
Now, geoscientists have a bad habit of turning a perfectly good adjective that ends in –ic into a noun.
We need to reprocess the seismic.
The logs from the washed out zones made it impossible to obtain a synthetic.
We need to reprocess the seismic data.
The logs from the washed out zones made it impossible to obtain a synthetic seismogram.
If in doubt, you can always ask me. I enjoy getting questions from the Peanut Gallery.