Among the commonly confused word pairings, "into" and "in to" are right there at the top. Do you turn in to the driveway or into the driveway? Do you log in to your computer or log into your computer? And does it even matter which way it's written since it sounds the same both ways?
First, a review
As with many of these commonly confused words, the answer to the riddle of which to use often lies in revisiting grammar rules that many of us simply forgot after middle school. For this particular commonly confused pairing, we need to take a look at what makes a preposition and how it functions in a sentence.
Prepositions
You might remember the grade-school textbook graphics of prepositions as positioning words, meaning they were used to show spatial relationships between objects. A cat might be in a window, on a windowsill, under a ledge, stretched around a pole, on a fence, or by a door.
Prepositions also show temporal (time-based) relationships. For example, this morning, I had coffee before I started writing, but after my alarm went off. During my lunch break, I read the news until it was time to write again.
From that quick review of prepositions you'll understand that "into" is a preposition and is used to show positioning—or more specifically, the literal placement of an object within another object. When you write a letter, you place it into an envelope, and then put the envelope into a mailbox. However, when you were driving along on the street and turned in to the post office parking lot to mail it, it became a situation where "into" as a preposition didn't fit. Think of "into" as something being placed literally inside something else.
Now, here's the exception to the rule
It wouldn't be English grammar if there weren't some exceptions somewhere to the rules of "into" being a preposition. "Into" showing transformation is one such exception. For example, a caterpillar turns into a butterfly. Fairy Godmother transformed Cinderella's rags into a beautiful ball gown.
When "in" and "to" end up together
Obviously, "in" and "to" are also prepositions and can also be used as adverbs. It would follow that there are instances when the two words will be together in a sentence, such as "I dropped in to make sure you're okay." In this sentence, "to" is part of the infinitive phrase "to make," so it would be incorrect to combine it with "in" typographically—even if the ear can't hear the difference.
Here are some more examples of "in" and "to" being separated in the sentence:
- Sarah turned her car in to the parking lot. (Note that since Sarah cannot literally be inside of the parking lot and she cannot transform her car into a parking lot, "in" and "to" separated make logical sense.)
- Can you tune in to the radio program next Wednesday at 9 pm?
- Log in to the admin portal of the website to change your password.
A final note
As with any commonly confused pair of words, taking a moment to consider the grammar rules behind the mystery is the easiest way to make sure you're using each correctly when you write. Sometimes, all it takes is a quick review of grammar rules you learned in elementary and middle school to choose the best word and once you've done this—the choice is clear.