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I am struggling to understand when to use fallback and when fall back (with a space).

Basically I have to say

This application implements a fallback [without space?] scheme: the application will fall back [with space?] to the next option if the first wasn't sufficient.

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closed as general reference by RegDwigнt Nov 8 '12 at 0:50

This question is too basic; it can be definitively and permanently answered by a single link to a standard internet reference source designed specifically to find that type of information.If this question can be reworded to fit the rules in the help center, please edit the question.

Fallback: noun, adjective. Fall back: verb. Same as with login vs. log in, backup vs. back up, etc. Really straightforward. – RegDwigнt Nov 8 '12 at 0:50
up vote 3 down vote accepted

In general, grammatically, fallback is a single word, normally a noun. The meanings are what you see on the wikipedia page and notice that in all cases, they're nouns. On the other hand, fall back is two separate words, a verb and an adverb (except in the case of the fall back and forward protocol). So you can fall back, but you can't fallback. You can have fallback, but you can't have fall back.

In the context of data communications, "fallback" is an algorithm used in some protocols. As a verb, "fall back" is used. As a noun, "fallback" is used with no space. So a modem will fall back to a lower speed. The amount of fallback is negotiated between the communicating modems.

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