Page 329 - Practical English Usage 3ed - Michael Swan, Oxford

313 know
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know how + infinitive
Know is not followed directly by infinitives. We use know how to (see 286).
I know how to make Spanish omelettes. (NOT { lenew t8 make . ..) object + infinitive
In a formal style, know is sometimes followed by object + infinitive. They knew him to be a dangerous criminal.
The passive equivalent is quite common in a formal style.
He was known to be a dangerous criminal.
In a less formal style, that-clauses are more usual.
They knew that he was a dangerous criminal.
Know means 'experience' in the common structure I've neuer known + object + infinitive; an infinitive without to is possible in British English.
I've never known it (to) rain like this.
tenses
Know cannot usually be used in progressive forms (see 471). I know exactly what you mean. (NOT .: am kn6l:fJing . ..)
A present perfect tense is used to say how long one has known somebody or something. (See 460 for more details.)
We've known each other since 1994. (NOT We lenew each ether since 1994.) know and know about/of
Know + object is used mainly to talk about knowledge that comes from direct personal experience. In other cases, we normally use know about!of, have heard ofor another structure. Compare:
You don't know my mother, do you? - No, I've never met her.
We all know about Abraham Lincoln. (NOT We all kil8W 14bmham Lillooln.)
know and find out etc
Know is not normally used to talk about finding something out: to know something is to have learnt it, not to learn it. To talk about getting knowledge we can use for example find out, get to know, learn, hear, can tell.
She's married. - Where did you find that out? (NOT ••• Vlhere did yolt lenow thaf?)
I want to travel round the world and get to know people from different countries. (NOT ..• anti lenew people . ..)
He's from Liverpool, as you can teU from his accent. (NOT ••• as}'B1t eall ienewjr8m hi.! aeeent.)
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6 IknowandIknowit
Note the difference between these two short answers.
I know refers to facts - it could be completed by a that-clause. You're late. -1 know. (= I know that I'm late.)
I know it generally refers to things - it replaces a noun.
I went to a nice restaurant called The Elizabeth last night. -1 know it.
(= I know the restaurant.) For ways of using YOII kllow, see 157.
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