I've come to think that the expression "I should think" means "it's highly possible" or "by the look of it" or something similar. Does my observation ring true ? Is it accurate at all ?

Here are a few examples where I encountered this expression:


A:She's upset

B:I should think she is (by the look of it she is ?)

2. Given that about 50 percent of scientists are religious, I should think they would welcome such a possibility (it's highly possible they would welcome it ?)

Thanks !
In my humble Finnish opinion I should think almost always means exactly the same as I think. It's mostly British, as far as I know.

I've always taken this expression to mean something like:
1) I certainly hope...
2) You're clearly justified in...
3) You have every right to...
4) They definitely should...

So, your examples could be expressed as follows (these are not exhaustive, just representative):

She certainly has every right to be upset.
She definitely should be upset.

Given...they certainly should welcome...
Given...they have every right to welcome...
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Thanks a lot, guys !
Long, long ago, in a land far, far, away, should (shall) was used in the first person, while would (will) was used in the second and third person. They were reversed to denote emphasis. My grammar teacher back in the Middle Ages insisted that Macarthur's "I shall return" should have been "I will return", because he wanted to be emphatic and used the wrong form, thinking he was being emphatic. These distinctions have largely vanished from modern use in AmEng.

Because "should" can also mean "ought to", it can be a bit confusing.

I should think he'd be tired of her by now ~ I should try to eat more vegetables.
MrPernickety"I should think" means "it's highly possible"
I would not put it that way. Your other suggestion "by the look of it" is closer. I'd say it's more like noting that something is obvious, that there is a good reason to believe it or expect it. It may indicate that the associated remark is an understatement. Note the stress pattern in the following.

I should think so, I should hope so, I should say so.

-- She thinks she'll have to apologize for what she said.
-- I should hope so. [Isn't it obvious that she should apologize? After what she said, she should be on her knees begging for forgiveness!]

-- Peter was a bit nervous during his presentation.
-- I should say so. [A bit nervous? It's obvious. He was shaking from head to foot!]

-- Larry just won $65 million in the lotto. I'll bet he's is going to celebrate for days.
-- I should think so. [It's obvious this situation calls for celebration. Maybe Larry will be celebrating for months -- not just days!]

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according to Macmillan Advanced Language Practice "I should think" is used to make an opinion less direct. So I quess it's almost the same as "I think".