Is the expression “one and the same” or “one in the same”?

Which is correct?

Microsoft’s approach with Windows 8 is that tablets and PCs are ____________: same interface, same apps, same touch-screen capabilities.

a. one and the same
b. one in the same

Answer: a.

Explanation:
The expression is “one and the same.” It uses reiteration for emphasis. Peter Parker and Spiderman, for example: They are one and they are the same. Which is problematic if they’re invited to the same cocktail party: Two invitations, one dude.

I have to admit, I was shocked — shocked! — by how many people get this one wrong. Drum roll, please …

Google poll:
One and the same: 245,000,000 results
One in the same: 1,920,000,000 results

I blame this, as usual, on so many more people writing than reading. Those non-reading writers hear an expression but don’t see it in print and so they don’t understand what they’re hearing. A lot of the people using the expression “one in the same” online are wondering what it means. Well, no wonder — it doesn’t mean anything at all!

Paul Brians includes “one in the same” in his Common Errors in English Usage.

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