A person who cognizes or becomes aware of something; one who has knowledge or awareness of something.
From 'cognize' plus the suffix '-er' (one who does), following standard English agent noun patterns. Used in philosophical and legal contexts to describe the active party in an act of knowing.
Every time someone learns something new, they're technically a 'cognizer,' but you'll almost never hear it used outside philosophy or law classes—it's one of those perfectly constructed words that English decided it didn't really need!
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