This document summarizes the use of modal verbs - would, could, should, and must - in first conditional sentences with "if". It provides examples of how each modal verb is used to express possibility, obligation, or recommendations when used with "if", such as "I would visit her if I had time" and "You should do it if you're good at it." It also explains how must can express obligations or prohibitions in a conditional sentence, like "If you must go, then go."

1. First conditional (If )with modals verbs would, could, should