When expressing certainty about something, instead of always using the phrase "are certain of," there are a variety of synonyms to choose from. For example, you could say "evince confidence," "believe without a doubt," "assure oneself," "have faith in," or "feel sure about." These alternatives can help convey a sense of conviction or assurance about a particular fact or situation. Whether you're writing an academic paper or having a conversation with a friend, selecting appropriate synonyms for "are certain of" can also add variety to your language, making your writing or speech more interesting and engaging.