theo·rize theorizes theorizing theorized in BRIT, also use theorise If you theorize that something is true or theorize about it, you develop an abstract idea or set of ideas about something in order to explain it. Police are theorizing that the killers may be posing as hitchhikers By studying the way people behave, we can theorize about what is going on in their mind. + theorizing theo·riz·ing This was no time for theorizing. to think of a possible explanation for an event or fact theorize that