Capitalize the first word of every sentence. This simple rule marks the start of a new thought and helps readers see where one sentence ends and the next begins, which is the foundation of clear writing. After a period, question mark, or exclamation point, you typically begin the next sentence with a capital letter. When a colon introduces material, capitalization after the colon depends on whether what follows is a complete sentence; if it’s a full sentence, some styles may capitalize, but if it’s a list or fragment, you don’t. Because the question asks for a straightforward rule about sentences and colons, the general guideline to capitalize the first word of every sentence is the most reliable and widely taught rule for everyday writing. The other options go beyond or misstate this guidance: capitalizing every word or every first letter of every word isn’t correct for standard sentence case, and treating all words after a colon as capitalized ignores the common distinction between complete sentences and lists or fragments.