This document discusses modals of deduction in English, including might/may, can't, must, and can't vs must. It explains that might/may indicate something is possibly true, can't shows something is impossible/not true, and must means something is sure to be true. It provides examples for each modal. The document also notes that could is used instead of might/may in positive sentences, and that be + gerund is often used after modals of deduction to indicate an action.