Is "That would be great" conveying a touch of unwillingness? [duplicate]

Possible Duplicate:
Should I use “will” or “would” when I suggest that something will/would come in handy?

For example:

Tom: Hey, will you be free tomorrow night to catch a movie together?
Jane: That will be great! / That would be great!

Often I see no difference. Yet one day it occurs to me that saying "would be great" sounds less certain than does "will be great". I was wondering whether this reply indicates that Jane cannot guarantee that she will make it tomorrow? Or is it totally out of politeness to say so rather than "will be great"?

The auxiliary would is in preterite form with modal function, showing that the scenario is a contemplated or counterfactual one, rather than a certainty. The overall construction is called the modal preterite. So the part in brackets is understood.

That would be great [if it happened].

The second thing that the response does is that it does not answer the question directly. Following the maxim: be relevant, you assume that the responder is, by not answering the question directly, trying to hint something indirectly. Namely:

I am withholding comment about whether I will be free.

As other commenters note, the tone of voice might help one to guess why the there is no comment about availability: (a) the person was so excited about the chance and just responded candidly, without thinking about how to be informative, (b) the person would have to extricate himself/herself from other responsibilities in order to go, but truly is willing, (c) the person may simply "not be free" because of lack of interest or unbreakable alternate commitments.

There's no withholding of enthusiasm or certainty in saying "That would be great." The "would" is an acknowledgement that the other person is making a choice and doesn't have to do it, not a reservation on my part.

Jane's use of the conditional would here would be more in line with Tom's question. If Tom had said something more indicative, such as

I'm taking you to the movies tomorrow.

Jane would be justified in saying

That will be great.

because both are statements indicating things that will happen, not that they might happen.

Still, Jane could still use would even in that sentence.

Note that much depends on tone: how she says it. Either sentence could be stated as irony, meaning the opposite of the literal wording. Or the tone could express anything fromn doubt and dissatisfaction to absolute approval and delight.

I believe this question is not really about syntactic analysis at its heart, but of social pragmatics.

Consider the following:

Open the door!
Open the door.
Please open the door.
I would appreciate it if you would open the door.
Would you mind opening the door?

All of these are clearly requests (or imperatives) for the same action, but they are ordered from most direct to most indirect, and also from least polite to most polite, especially when the addressee has higher social status (as a parent or teacher, for example).

"That would be great" is a polite and respectful way of saying "Yes" to the proposal, somewhat more so than "That will be great!" and much more than a plain "Yes".

It's been 25 years since my LING major, so I forget the name of this language feature, but I am sure it has one.