Of the four, “quite” is the most affirmative. It implies a high degree of certainty.

I would say that “rather” and “fairly” are roughly interchangeable. Both are tentative assertions.

The same could be said for “pretty”, but it tends to be used more informally.

I agree with @thorninmud. If I had to give them a rank ordering, however, I would suggest that “quite” is the strongest, followed by “rather,” followed by “fairly,” followed by “pretty.” To me, “I’m fairly sure” and “I’m pretty sure” both sound a bit more tentative than “I am quite sure” and “I am rather sure.” The first two sound like you might be hedging your bets, whereas the latter sound like you are trying to convince someone.

I am quite sure I know the answer to this question. (I would bet the farm on it.)

I am pretty sure I know the answer. (I would bet only the ox-driven plow.)

I am rather sure (Personally I would not use “rather” as a qualifying adjective since it does’t really qualify anything.)

I am fairly sure, but to be on the safe side, I would bet nothing.

Probably if not certainly @gailcalled‘s answer is spot on.

Milo here: I’m pretty sure you are right.

I’m also quite sure Gail is correct, however, I would say that rather should be used gingerly, as it has a bit of an old-fashioned connotation. I’m pretty sure about this. Quite sure, in fact, I’m fairly sure that only rather wouldn’t be used in this case. One could say “I am rather sure” – but it just doesn’t sound right. Right?

@gailcalled As one who uses “rather” rather a lot, I am curious about your distaste for it. Could you say more?

it’s too vague. I’m rather unclear about my answer so I will fudge.

I’m rather hot.

I’m rather fond of oatmeal, but only on odd days.

I’m rather short-tempered today. Be very afraid, or not?

I’m fairly sure that I am beginning to feel the say way about “fairly.”

@gailcalled Perhaps. I tend to use the words in the strict ordering I gave above, so they do not seem all that vague to me. Indeed, the statement “I’m rather fond of oatmeal, but only on odd days” seems quite infelicitous to me.

Actually, it seems rather infelicitous to me, but I would not want you to think I was being vague.

I agree; I meant it to sound infelicitous.

I either like oatmeal or I don’t.

I’m either cranky or I’m not.

No one is going to call you (or me) out over this issue.

I am absolutely sure that I have to face the litter box this minute rather than stalling. Milo is getting really rather shirty.

@gailcalled But if it’s infelicitous, that suggests it is an improper use of “rather,” not that “rather” is itself improper to use. Are you perhaps saying that you think “rather” is abused too often and that is why you have a distaste for it?

@SavoirFaire: To be honest, I am no longer sure how I feel about any of this.

There is so much waffling today and so few elegant orators that I have become almost Prussian in my distaste for the unnecessary qualifiers.

You I consider among the elegant users of the language. Carte blanche, cher.

It’s what upper class British people say after every sentence. Mmm, yes, quite, indeed, rather.

By the way, is rather not also sometimes used as preference?

@rebbel Yes, it originally meant “sooner, or more quickly”, so it could be used in the sense that “I’d more quickly go to the movies than to school”. In the usage this question is referring to, it implies that “I’d more readily describe it this way (than that way)”.

Interesting, @thorninmud, thanks for that.

@gailcalled Ah, I see. “Use it well or not at all.” Hard to argue with that.

Many words don’t have precise meanings, it depends on the context.

About a gnats nadge.

http://forum.wordreference.com/showthread.php?t=851856

There are several links to forum discussions inside this link that may be of help to you. Just scroll down and you’ll see nine blue links.

[mod says] I’m rather pretty fairly quite fond of this question, so this is our Question of the Day!

I think they are mostly interchangeable, at least thats how I use them. But there are slight variations. Quite and rather = VERY, to me. That is quite delicious! I was rather impressed! Pretty, I use like “The cake was pretty good” as in MAYBE it could have been better. Fairly…..is like “kind of”....I’m fairly certain that…..it’s like a 50/50 chance.

Again, thats just how I use these four words. I’m sure it’s vastly different across the board of english speakers though.

Great question!

When I read “rather” I hear a British accent in my head. You can also do it with “quite” but it doesn’t have the same edge.

e.g. “Dear – I’m rather chilly, would you mind turning up the heat?”
Or: “Rather a long shot, no?”

Note that “rather” in another context is used as a comparative, as in:
“Would you like to go out to see a movie?”
“I’d rather stay at home.”
Therefore, even when it’s used as a qualifier to express “to some extent”—(e.g. “I found the party rather boring”) in my mind there’s still another alternative implied.

Incidentally, if you asked me what is stronger : “I found the party rather boring” or “I found the party quite boring”; I would say that “rather boring” is more scathing. I wonder if it’s the long vowels in that phrase that make it so? Where as “quite” with the short ‘t’ has a crisp sound to it.

Here’s a tmely article from today’s CNN’s politicalticker.blogs that quotes from “The National Review,” whose opinions I usually do not agree with but whose style and use of language I have admired.

http://politicalticker.blogs.cnn.com/2012/02/13/national-review-calls-for-gingrich-to-leave-race/

“While the magazine complimented Santorum as “conducting himself rather impressively” by showing some humility and emphasizing the declining stability of the middle class as a key issue, it said his most immediate challenge is “proving he can run a national campaign.”

I really dislike reading that Santorum conducts “himself rather impressively”. He is either impressive or unimpressive. I’d rather see less waffling.

And yet, if someone says to me “you look quite nice” or “it was quite well written”. I hear… you look… okay… or your writing is decent but not great.

And “that’s rather nice!” Said with the right inflection can mean that’s wonderful or with the wrong inflection “that’s meh… okay”.

I have this argument with my husband ‘fairly’ regularly. Like @gailcalled says, I want to hear or read. You write well. You look good. The additional words are an example of hedging to my mind.