"I knew him for three years."

[birgit33]

"I knew him for 3 years." Is this incorrect and does it have to be "I have known him for 3 years"?

 

[Barb_D]

Is he dead?

 

[birgit33]

He sadly passed away...:-(

 

[HanibalII]

Is he dead?

Sorry, but what does that have to do with it?

I could say 'I knew Joe Blow for 3 years. Then he moved away'.

I would use 'knew' because you may/may not know him after he moved away.

 

[5jj]

Sorry, but what does that have to do with it?

Obviously, to many of us at least, quite a bit. His demise is one clear reason for using the past simple. There are others, as you pointed out, but you seem to suggest that Barb's question was irrelevant. I would have posted a similar message if Barb had not got there first.

 

[Raymott]

Sorry, but what does that have to do with it?

It doesn't necessarily make a difference. But it is a way of letting the OP know that such a factor plays a role in the syntax. The OP then thinks about the question, and realises other contextual factors that may be relevant.

 

[Barb_D]

He sadly passed away...:-(

Then you knew him for three years.

The present perfect (I have known him) is suitable only when you continue to know him now and possibly into the future.

Sorry for your loss.