What are stem changers??

Question

ex) jugar-(to play) juego,juegas,juega,jugamos,juegan querer (to want) quiero,quieres,quiere, queremos,quieren

Answer 1

It seems to me that you've answered your own question. Stem changing verbs change from what you'd expect to a slightly different pronunciation and spelling.

People have opined that this is usually if not always done because keeping the verb completely regular would result in some undesirable word being formed. (Either causing identical spelling to some other word, or causing some pronunciation difficulty.)

So in the case of querer, one would think it would be-

quero, queres, quere, queremos, queren.

But the stem changes from e to ie... thus quiero, etc.