Any Korean verb form used in a Korean sentence has two parts to it: a BASE and an ENDING. A base is not complete, ready for use, until it is finished off with an ending; and obviously, an ending must be attached to something before it can be put into a sentence (just as you don’t use the English endings -ing or -ed in mid-air). In summarizing verb forms, then, it is convenient to split the discussion into the two large categories BASES and ENDINGS.