Yahoo: The Early Warning Signs of COPD You Need To Know—and How It Differs From Bronchitis The Early Warning Signs of COPD You Need To Know—and How It Differs From Bronchitis Recently one of my friends told me that there is distinct difference between 'know of something' and 'know about something' expressions. 'know of' is used when you have personal experience with wha... Why do you think that He doesn't know him from his schooldays means that he does know him?

Understanding the Context

It would only have that sense if you added something like In fact, he first met him at university. Should I use "did you know" or "do you know" to introduce a fact? I've only seen "did you know" in action. My logical deduction is that before the "question" (which is not much of a question because you're not asking for an answer), you wouldn't have been sure whether the listener'd known about what you're about to say or not.

Key Insights

If you know about a subject, you have studied it or taken an interest in it, and understand part or all of it. Hire someone with experience, someone who knows about real estate. I already know how to turn on the television. I know how to drive a car. You would use the present perfect to express something that happened previously, without specifying the time.

Final Thoughts

You'll only use the present perfect and "already" when expressing previous events relative to the present. I have been to France before. "Know about" vs. "know of" - English Language & Usage Stack Exchange