Questioning Conceptual Continuity: Dante and Descartes

As I unpack boxes and returnt them to shelves, I'm finding much food for thought. One of my daughters asked me--no joke--if _The Divine Comedy_ was funny because--get this--the pictures didn't look funny at all! (Inferno don't ya know?)

Clearly "Comedy" expresses a different property now than it did in the past (tough there is a clear family resemblence [warning: non-transitive]. I wonder why so many philosophers assume so easily--without argument or marshaling historical or linguistic evidence--that "knowledge" expresses the same property now as it used to (pretending that it only ever expressed one invariant property).