I could not/did not...

[thehammer]

Which one is correct?

1- My friend told me that God is real. So I searched on the internet regarding the existence of God. But I could not/did not find any substantial evidence of God's existence.

 

[Barque]

They both work in that context.

 

[thehammer]

They both work in that context.

Here are some other examples:

2- I didn't/couldn't respond to other questions because I didn't have enough time.

3- Yesterday I and my friend was talking in the park. I couldn't/didn't understand a word he said.

4- I asked John's mom where he is. His mom said he was playing on the ground. When I reched there I couldn't/didn't see him.

 

[Barque]

2- I didn't/couldn't respond to other questions because I didn't have enough time.

They both work.
I couldn't = I was unable to.
I didn't = I did not.

They often effectively have the same meaning, though not always.

3- Yesterday I and my friend and I were was talking in the park. I couldn't/didn't understand a word he said.

Again, both "couldn't" and "didn't" are possible here.

It also depends on what you mean by "understand".

Was he slurring because he was drunk (and you couldn't make out his words)? I'd use "couldn't".
Or was he using long words that you didn't know the meaning of, and talking about some scientific concept that you couldn't follow? Both "couldn't" and "didn't" are possible.

4- I asked John's mom where he was is. His mom She said he was playing at on the ground. But when When I went reched there I couldn't/didn't see him.

Here, I'd prefer "couldn't". You were trying to find him but you couldn't. "Didn't" isn't wrong here however.

It'd be simpler to just replace the third sentence in this example 4 with "But I couldn't find him there". It'd be implied that you went there.

(By the way you've made this mistake a few times--it's always "my friend and I" or "John and I", and not "I and my friend" or "I and John".)

 

[thehammer]

Hello Barque. Are both correct in the following sentence?

- Just because you didn't/couldn't see him there did not mean he wasn't there.

 

[Barque]

Just because you didn't/couldn't see him there did not mean he wasn't there.

What's the context? This was obviously said in reply to something. It wouldn't have been said spontaneously.

 

[Tarheel]

Try: "Just because you didn't see him that doesn't mean he wasn't there."

I would ask if I could use either one.