Login / log-in / log in (along with other similar examples such as: signin / sign-in / sign in, signup / sign-up / signup, signout / sign-out / sign out, logout / log-out / logout) are known to cause a great deal of confusion to writers. Take: Login / log-in and log in for example. Though we commonly use this word virtually every day, many of us are not entirely certain whether this word is actually one word at all, or two.

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Grammar rules

Login

If you spell ‘login’ as one word, then it’s a noun or an adjective. For instance, your ‘login’ (noun) is the credential that you use to log into your account. Those credential can also be called ‘login credentials’, in which case you are using ‘login’ as an adjective. You would enter that info into the ‘login page’, which would be another example of ‘login’ as an adjective.

Log-in

The hyphenated form is an alternative spelling for the unhyphenated spelling. Hyphens should be used to link two words together to allow the reader to know that the words in question are linked and to avoid confusion. In the English language, it has often happened that some once hyphenated words at some point lose the hyphen in favor of the unhyphenated spelling. For example, the term ‘email’ has progressively gained popularity against the formally correct version ‘e-mail’ and has now become the standard.
Whatever spelling you prefer, if you use the hyphenated form, you are referring to the name or to the adjective. The hyphenated spelling is more frequently preferred by editorially conservative publishers (e.g. it is found in the New York Times), nevertheless most of the top world publishers in the English language use the unhyphenated form. I prefer to cut it shorter and avoid the hyphen unless it’s necessary.

Log in

If you are spelling it as two words, then ‘log in’ is a verb, more precisely a prepositional verb. For example, you ‘log in’ (verb) with your ‘login’ (adjective) credentials.

Rule of thumb: if the word is a noun or adjective, you should use one word (login), for verbs, use two words (log in).


Examples

By now things are probably much clearer, but just to ensure that there’s no confusion, we’ll now look at a few examples:

Login – Login comes in the form of one word and can either be an adjective or a noun. In the example below is an adjective.

Log-in – Can be a noun or verb, here it is used as an adjective:

Log in – Log in is a verb:

The same rules apply to other similar examples, such as:

Sign-in / sign in - In this case the hyphenated form is the only acceptable one, while the unhyphenated doesn’t exist. Two separate words are used when a verb.

Signup (sign-up) / sign up - As in the case of login (log-in) / log in use as one word when a noun or adjective (with the hyphenated alternative) and two words when a verb.

Signout (sign-out) / sign out - Again, one word when a noun or adjective (with the hyphenated version as an option) and two words when a verb.

Signoff (sign-off) / sign off - Once more, one word when a noun or adjective (with the hyphenated alternative) and two words when a verb.

Logout (log-out) / ‘log out’ - The same as above, it’s one word when a noun or adjective (with the hyphenated alternative) and two words when a verb.

Similarly to the above examples, also words like backup, signoff, lineup, makeup and workout are nouns (or adjectives, while the two words versions are verbs: back up, sign off, line up, make up and work out.


Ludwig’s wrap up

As a rule of thumb, go for the version without hyphen if it’s a noun or adjective and for the two words if it’s a verb. Now it’s time that you log in to Ludwig and start searching for the perfect sentence.