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...
Know in (1) refers to the clause that comes right before it, so there's no pronoun necessary -- it's essentially a transform of I know it's your job. In (2), however, the object of know is not indicated, as you point out, so something must be provided.
Possibly, "I do know that" can in fact only be used, when, you are answering the question of whether or not you know the issue at hand (or your knowledge has been called in to question, and you are answering that challenge). Let's say "out of the blue" you wanted to state that "you know that" -- and you wanted an emphatic version.
Why do you think that He doesn't know him from his schooldays means that he does know him? It would only have that sense if you added something like In fact, he first met him at university.
Therefore, saying "did you know" asks if you have previously known something. "Do" is the present tense, so saying "do you know" would ask if you currently know.
Thus, "As far as I know, Bob is happy" over "Bob is happy, so far as I know". They are equivalent in meaning therefore, but choice of one over another betrays, for me, certain prejudices. I also sense that "so far as" sounds slightly antiquated and is losing ground.
It's not just you that doesn't know. Now, according to owl.purdue.edu, we should use "doesn't" when the subject is singular (except when the subject is "you" or "I"), and "don't" otherwise. But in the example above, I am having a hard time figuring out what exactly the subject is and whether it is singular.
For a non-native speaker like me, I am always wondering how to use you know correctly, as in the following sentence: Alright, well, for example, like on Saturdays, y’know, what I liked to do ...
