Before going any further, it will be helpful for you to learn how the Greek language turned nouns into adjectives. Earlier in the course, we saw that this was quite a complex problem in Latin—it formed the subject matter of a whole chapter (Part I, Chapter 5). You may be relieved to discover that the principle is much simpler in Greek.
The straightforward rule for turning a Greek noun into an adjective is to add -ικος to the noun base; this will produce an English derivative in -ic:
|κεφαλη||“head”||κεφαλικος||“pertaining to the head”||> E||cephalic|
|φωνη||“voice”||φωνικος||“pertaining to the voice”||phonic|
|ψυχη||“soul”||ψυχικος||“pertaining to the soul”||psychic|
|μουσα||“muse”||μουσικος||“pertaining to the muse”||music|
There is only one exception to this rule, and it is phonetically consistent. If the noun base ends in the vowel iota (ι), the adjective forming suffix is not -ικος but -ακος; in this case, the English derivative will end in -ac:
|καρδι-α||“heart”||καρδι-ακος||“pertaining to the heart”||> E||cardiac|
As you have perhaps noticed already, there is an odd complication to this otherwise very easy rule. Because of the profound influence of Latin on all English vocabulary, our English adjectival derivatives from Greek nouns often display the suffix -al, which you will shrewdly (and correctly) identify as the legacy of the Latin suffix –alis. Thus the Greek adjective σφαιρικος (“like a ball”) has acquired an extra syllable in assuming its English form spherical. Educated ancient Romans would have shunned such redundant hybrids; the extra suffix has usually been added by speakers of English. But sometimes there was a good historical reason for the additional element; for example, once the feminine adjective musica (> E music) had become a Late Latin noun, the adjective musicalis (> E musical) made perfectly good sense. In English, it is not uncommon to find the pure Greek derivative co-existing with its hybrid counterpart. Thus the 1st declension Greek noun λυρα (“lyre”) has two English adjectival derivatives: lyric (< G λυρικος) and lyrical, with the hybrid Latin suffix added. Both words appear to have entered English in the same year (1581). The similar English pair of adjectives comic and comical are derived from a 2nd declension Greek noun (κωμος); comical is actually the older of the two English words.