'I thought', 'I would think', 'I would have thought'

Question

I'm going to show you three examples.

1. A - Have you got any change?
    B - Do I have change? What for?
    A - For the vending machine!
           I would have thought that was pretty obvious.
: I think it's sufficient to just say,
  "I thought that was pretty obvious."
  because literally 'I' thought so in the past, which is a simple fact, but now I don't.
  And "I would think that as pretty obvious." is possible in the context?
  If so, what are the differences among them?

2. Let's say there are two kids playing in the garden
     and their mum comes out to tell them in for dinner.
     But the kids have gone somewhere, so she starts going around for them.
     In some minutes, she finds the two and says.
     "I would have known."
     Why does she talk like that? What's the nuance?
      I think it will do to say,
    "I knew you would be here."
      I wonder if "I would know" is a possible subsitute for the highlighted sentence.
      If it could be, what are the differences among the three?

3. A - Was the party great?
     B - I don't / wouldn't know. I wasn't there.
: I think if B goes for "I don't know",
   it will mean he's just saying the plain fact that he wasn't there.
  What if B replies, "I wouldn't know"?
  What's the difference?
   And is "I wouldn't have known" possible here?
   If so, what are the differences?

I hear 'would do / would have done' structure is closely related to a hypothetical if,
but I can't seem to figure it out.
I was guessing 'would have done' might mean speculating about the past,
I've come to think it can't explain 'would do' option.

Help me out with this.
Thank you all.

Answer 1

1. I’m sure all of these variations are commonly used and understood to mean roughly the same thing. “I would have thought…” essentially means “I believe you should have understood what I meant,” or “that should be obvious.” “I thought that was obvious” is a simple declaration that sounds more like the speaker actually gave the matter some thought.

2. “I should [not “would”] have known,” means that she realizes, after finding the boys, that she should have expected to find them where she did. “I knew you would be here” is similar, but means that she went straight to wherever she found the boys based on her knowledge of their habits. Both phrases might imply some disapproval of their being there. “I would know” (or “I should know”) is not a possible substitute for your sentence. As a complete clause, it’s more like “you can take my word for it,” or “take it from me,” implying some experience of a situation, often said ruefully or with a little chagrin.

3. “I don’t/wouldn’t know”: There wouldn’t be much reason to answer “I don’t know”; it’s more direct to just say that you weren’t there. “I wouldn’t know” might be employed where there’s some displeasure, like if B thought he should have been invited to the party but wasn’t. The “would” in “I wouldn’t know” is present tense; “I wouldn’t have known” is not possible here because it puts it in the past tense.

Answer 2

"I would think" and "I would have thought" are instances of the common use of the conditional to soften assertions. This can be useful in establishing plausible deniability or saving face in case the assertion proves to be incorrect. It can also help reduce the harshness of a correction (that is, saying "no, three squared is nine" is blunt and might offend, but "I would have thought that three squared is nine." is less blunt and more likely to be accepted.)

Stephen Pinker touches on this some of his writing, and in this talk he discusses how it is related to people's managing their relationships with one another: http://www.ted.com/talks/steven_pinker_on_language_and_thought