Know

We commonly use the verb know with a noun phrase, with a that-clause or with a wh-clause (e.g. who, where, why):

Do you know the music shop just by the market square? (+ object)

We know that this must be a difficult decision for you. (+ that clause)

Do you know where to buy batteries for the watch? (+ wh-clause)

We don’t use continuous forms of know:

She’s a really good teacher and knows the names of over two hundred of her students.

Not: … and is knowing the names of ….

We’ve known each other since we were children.

Not: We’ve been knowing each other …

Know how + infinitive

We do not commonly use know + to-infinitive. We use know how + to-infinitive:

Does he know how to play classical guitar music?

Not: Does he know to play …

Know + object + infinitive

In very formal English, we use know + object + to-infinitive:

[extract from a reference for a job]

I have worked with John Davidson for five years and know him to be reliable and hard-working.

Weather experts have never known it to snow as heavily as it has this spring.

Know without an object

To refer to general knowledge, we use know without an object:

A:
They’re opening a new terminal at Amsterdam airport.

B:
Yes, Iknow. (I know that they are opening a new terminal.)

We use know + object to refer to what we know from personal experience:

A:
They’re opening a new terminal at Amsterdam airport.

B:
Yes, Iknowit. (I know the one you mean. I have been there and seen the airport.)

We also sometimes use know about or know of when we say what we know from general experience (know of is more formal):

What do you know about the origins of the American Civil War?

Not: What do you know the origins …

You know

We use you know very often in speaking as a discourse marker. We use it to check that the people we are speaking to share the same knowledge as us and understand what we are saying:

It’s impossible to find time to go to the gym, you know, every day, isn’t it?