Can't think vs can't think of

[NAL123]

We both said we would like to see each other again and we went our separate ways. I sent him a text message the next day thanking him for a nice evening. Then, never heard back from him again. I can’t think of why he didn’t respond. I don’t want to be pushy and send him another message, but I don’t understand. We had a great time together. (Link here)

1) Can I also say here:

I can’t think why he didn’t respond.

My boyfriend's 30th birthday is coming up in March (I obviously plan trips well in advance). I want to take him somewhere memorable and fun but can't think of where. We love to travel and are open to anything. (Link here)

2) Can I also say here:

...but can't think where.

 

[jutfrank]

Before we answer, please tell us who wrote or said these words and where exactly you read or heard them. You must do this every time. Thank you.

 

[NAL123]

Before we answer, please tell us who wrote or said these words and where exactly you read or heard them. You must do this every time. Thank you.

Included the links in post #1.

 

[jutfrank]

1) Yes. In fact, it's better without 'of'.
2) No.

 

[NAL123]

1) Yes. In fact, it's better without 'of'.
2) No.

So, what's the difference between I can't think and I can't think of?

 

[jutfrank]

I can't think + 'wh'-clause

This semi-fixed expression requires a question word (followed by a clause), always uses 'I' as a subject, and has a meaning equivalent to 'I don't know' or 'I have no idea', and sometimes even 'I can't remember'. There's always an implicit question that is not stated.

I really can't think how that could've happened.
I can't think what they would've wanted.
I can't think why he didn't respond.
I can't think when it was.


think of [something]

This verb + prepositional phrase combination is not an expression at all, and has a meaning similar to 'invent' or 'come up with' or even 'choose'. The object of the preposition is also some kind of mental object:

I can't think of a good example.
I just thought of a country starting with 'O'!
I'm thinking of a number between one and ten.
Okay, I'll try to think of a game the kids can play in the car.

 

[NAL123]

I can't think + 'wh'-clause

This semi-fixed expression requires a question word (followed by a clause)

Is this the reason we cannot say "...but can't think where." in (2) in post #1 (there's no clause following the word "where")? Or is it because of the meaning of the expression "I can't think", meaning I don't know?

think of [something]

This verb + prepositional phrase combination is not an expression at all, and has a meaning similar to 'invent' or 'come up with' or even 'choose'. The object of the preposition is also some kind of mental object:

I can't think of a good example.
I just thought of a country starting with 'O'!
I'm thinking of a number between one and ten.
Okay, I'll try to think of a game the kids can play in the car.

Can we follow "think of" with a wh-clause?

 

[jutfrank]

Is this the reason we cannot say "...but can't think where." in (2) in post #1 (there's no clause following the word "where")?

No, that's not the reason because the clause doesn't have to be articulated to be still 'there'. The speaker here is trying to come up with an idea, so it would be better as: I can't think of anywhere (to take him).

Can we follow "think of" with a wh-clause?

It's possible, yes.