Predict

Only "will" is correct. "Should" does not predict a future event. You may express an opinion that he's obligated to change the policy, but that would not be a prediction.

You may also say, "I think it should happen," but I believe this is an expression of probability, which is not the same as an opinion that it will happen.

Edit. It's also p

AvangiYou may also say, "I think it should happen," but I believe this is an expression of probability, which is not the same as an opinion that it will happen.

Isn't prediction something about probability?

Many published books seem to show that 'prediction+should' might be acceptable:
http://books.google.com/books?q=%22prediction+that+*%22&lr=&as_brr=3&sa=N&start=0 

Anybody else? 

I originally saw this post as a question related to reported speech:

His prediction that the president will change the policy is unlikely to come true.
vs.
His prediction that the presdident would change the policy was unlikely to come true.

Should has nothing to do with prediction, but rather with obligation; it has not place in

Taka Isn't prediction something about probability?

Absolutely true! A prediction may be based on probability, but they're not synonymous. (It also may be based on astrology, or a flip of the coin.)

The second "should" use in my first reply was something like,

"Since their best player is injured, I think we shoul

Let me make it clear that my first choice is also 'will'. I'm just wondering why we cannot use 'should' here when we have this definition of The American Heritage:
2. Used to express probability or expectation: They should arrive at noon.
http://www.bartleby.com/61/83/S0368300.html

I don't believe anyone has said we can't. But your example was of the "fill in the blank" type.

"I predict that they should arrive at noon" is illogical. It must be, "I predict that they will arrive at noon."

Think about it.
You say, "I predict that they should arrive at noon."
They never show up at all!
Your friend says, "Ha!, I guess

There are four shoulds to consider.

1. "advisability" should. (should_a)

The president should_a change the policy. = It is advisable for the president to change the policy.

Advice is not prediction, so should_a can't be used. Would anyone predict something advisable? Doubtful. If I say, "You sh

Wow, that is quite an explanation. Thanks, Jim. I'm wondering if such 'should' of prediction is really only for scientific matters or not, but before that, let me ask about this.

CalifJimExpectation is not prediction. I can believe that something will happen (expect it) without saying so (predicting it).

When we predict something, do we really alwa