The building blocks of English

Affixes

-logical

Also ‑logic.

Relating to a branch of knowledge or experience.

Formed from nouns in ‑logy by replacing the last letter with ‑ical or ‑ic.

Many examples exist, of which a few are: astrological, biological, ecological, ideological, mineralogical, numerological, seismological, sociological, theological, and zoological.

Though ‑logical is the standard way of forming such adjectives, a few are also formed using ‑logic, such as hydrologic, morphologic, and physiologic. Adjectives sometimes exist in both spellings: geological and geologic; pharmacological and pharmacologic. In such cases, there is no clear distinction of sense, but the one ending in ‑logical is substantially more common.