Phonosemantic compound. 口 represents the meaning and a pictograph of an axe handle (丂) which is now written as 柯 represents the sound. Based on the original meaning "sing", now written as 歌. The current meaning "able to" is a phonetic loan.

Evolution

Oracle script

(~1250-1000 BC)

Bronze script

Late Western Zhou (~800 BC)

Seal script

Shuowen (~100 AD)

Clerical script

Eastern Han dynasty (25-220 AD)

Regular script

Modern

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