Well, word nerd, you've come up with a very good question.

Did you ever hear about the magician who was so talented that he could drive down the street and turn into a gas station? Of course, if he just wanted to get gas, he would turn in to a gas station.

It's a similar situation here.

In terms of grammar, "into" is a preposition which modifies the preceding verb or verb phrase. We normally use "into" to express motion or direction, such as "staring into the abyss" or "walking into the garage." But it can also indicate a change of state or modification of condition, like the story of Cinderella when a pumpkin was "turned into a carriage."

Using that paradigm, we could certainly think of "getting into graduate school" as a modification of condition. Just like someone can "slip into depression" or "fall into error," getting into graduate school could offer a new end state.

But most grammaticians would think of it differently. Getting in to grad school is not an end state; it's a process.

The phrase "in to" separates the words because the "in" and the "to" perform independent tasks. Sometimes the "in" is paried with an infinitive, such as "to wash" (e.g., "she came in to wash her hands"). But other times, the "in" is simply busy modifying the verb while the "to" offers a preposition with its own object. That is, you are "getting in" to some place (the "in" explains where you're getting), and the "to" reveals that the object of your intention is graduate school.

I love it, both grammatically and philosophically. We're combining an action ("getting in") with an intention ("to grad school"), just as the application process marries both your goal and the activities needed to achieve it.

Getting in to grad school: it's the only way to go.