When writing my Security Tutorials for www.asp.net, I often wrote sentences like the following: “To log in to the site, ...” Although sometimes I'd write it, “To log into the site, ...” and other times I'd use, “To login to the site...”
I can't say with certainty whether any one of these three are grammatically correct or if any are grammatically incorrect. My guess is that in the sentence above, “To login to the site...” is incorrect because, according to Dictionary.com, log in is a verb, while login is a noun. In other words, you would only use the word login in a sentence like, “Your login is comprised of a username, password, and PIN.“ That leads me to believe that the correct form is, “To log in to the site,“ but I'm sure someone out there can make a case for “To log into...“
In any case, I should have picked a particular approach and used it throughout, rather than varying the styles throughout the tutorial series. If it's any consolation, I assure you that the variance was done on a purely subconscious level.
All that being said, what do you prefer?
- To log in to the site...
- To log into the site...
- To login to the site...
The more I read it and think about it, I believe the latter one to be grammatically incorrect.
Another thing I noticed is that when I read them there is a very subtle pronounciation difference among the three sentences, although I don't know how clearly that difference translates into the spoken word. When pronouncing login I run the “g” and “in” together, like I'm speaking 1.5 syllables instead of two. Log in to are pronounced as three distinct words with a briefest of pauses between each, whereas log into is pronounced as two distinct words: “log” and “into,” with no pause between “in” and “to” (again, almost as if blurring the two words together into 1.5 syllables).