What does it mean for a Spanish verb to be irregular? Por ejemplo, I’m told by one source that “pagar” is irregular. Does this simply refer to the one spelling difference in preterite, yo pagué? I don’t consider this to make pagar irregular - like “hacer” or “dar” are irregular. It’s just the addition of a “u” for pronunciation/textual consistency - unlesss I’m missing some actual irregularity for pagar.