The English language. Many important people use it fluently.
Deep-seeded vs. deep-seated
Deep-seeded almost makes sense in a metaphorical way (though seeds sown too deeply won’t grow), but deep-seated is the term you’re looking for. The phrasal adjective (usually requiring a hyphen) simply indicates that something is seated (in the sense fixed firmly in place) deeply in something else. The OED defines it as having its seat far beneath the surface.
Those who pine for the oral cultures of Ye Olden Dayes can rejoice as we enter an era where many people are unfamiliar with common expressions in print and know them only by hearsay. The result is mistakes like “deep seeded.” The expression has nothing to do with a feeling being planted deep within one, but instead refers to its being seated firmly within one’s breast: “My aversion to anchovies is deep-seated.” Compounding their error, most people who misuse this phrase leave the hyphen out. Tennis players may be seeded, but not feelings.
"Is it deep-seeded or deep-seated?" Deep-seated, according to Webster's, means "deeply entrenched: ingrained." Deep-seeded has no dictionary entry. But we can see how one would make that mistake. Honestly, deep-seeded makes more sense. Deeply rooted, implanted, yada yada. However …
The notion that English should be spelled as it is pronounced is widespread, but history is against the reformers in most cases. Pronunciation is often a poor guide to spelling. The veneration of certain political movements for the teaching of reading through phonics is nicely caricatured by a t-shirt slogan I’ve seen: “Hukt awn fonix.”
