Whereof is an old-fashioned formal word meaning “of which” or “of what.” You might find it in older books, legal documents, or solemn ceremonies. When someone writes “the evidence whereof is clear,” they mean “the evidence of which is clear.”

The word appears in serious contexts where precision matters. A witness signing a document might write “in witness whereof, I set my hand,” meaning “as proof of which, I'm signing this.” The philosopher Ludwig Wittgenstein famously wrote, “Whereof one cannot speak, thereof one must be silent,” meaning roughly “about things we can't discuss clearly, we should stay quiet.”

Today, most people replace whereof with simpler phrases. Instead of saying “the matter whereof we speak,” you'd say “the matter we're talking about.” Instead of “the crime whereof he was accused,” you'd say “the crime of which he was accused” or just “the crime he was accused of.”

You'll still encounter whereof in formal speeches, older literature, legal papers, and philosophical writing. It adds a solemn, weighty tone. When you see it, pause and figure out what “of which” connects to. Understanding whereof helps you read older texts and appreciate how English has changed over time.