"An other" vs "another"

I just edited this answer on unix.sx. The original sentence was

But it won't transform it to an other format.

I changed this to

But it won't transform it to another format.

The second form is standard, but is the first correct?

Solution 1:

The string an other is vanishingly rare in English. In contrast another is positively pervasive. I think it would be fair to say that the second has eclipsed the first to the point of making the first unacceptable, even though it is a grammatical string.

Both an and another are members of the category of determiners, while other, on the other hand, is an adjective. There's no grammatical reason why DET + ADJ would be unacceptable. So, it must simply be a matter of convention that makes an other unacceptable...

Solution 2:

Here is a general rule of thumb: if you mean "a different [noun]", then it is more appropriate to use "an other"; if you mean "an additional [noun]", then it is more appropriate to use "another".

So in your example you should use "But it won't transform it to an other format."

Also take a look at Brett Reynolds' answer. It is good from a syntactical point of view.