Are "should" and "if" interchangeable at the beginning of a sentence? [duplicate]

Possible Duplicate:
A special use of “should”?

If "should" comes at the beginning of a sentence, and the sentence is not a question, then can it be replaced with "if?" Is there any difference at all?

Solution 1:

You can't simply swap the words, as they are grammatically different:

If the sky is blue...
Should the sky be blue...

Solution 2:

• "Should I..."
• "Were I to..."
• "If I..."

Or

• "Should it rain Saturday..."
• "Were it to rain Saturday..."
• "If it rains Saturday..."

These forms all convey the same meaning, but they are very different in style. The only form (of the above) that appears commonly is "If". The others sound formal / poetic / literary.

Solution 3:

They're different in the same sense that "Jane kicked the ball" and "The ball was kicked by Jane" are different. They mean the same thing, but the emphasis is different and often one is more appropriate than the other.