Don't confound the two. Eat is present, ate
is past. "I eat the bread" means that I am continuing the eating; "I
ate the bread" means that the act of eating is past. Eaten is the
perfect participle, but often eat is used instead, and as it has the
same pronunciation (et) of ate, care should be taken to distinguish the
past tense, I ate from the perfect I have eaten (eat).
