in to is used when the following word is an infinitive.

i.e. <i>come <b>in to</b> warm up, it's cold outside.</i>

while into is a preposition refering to a direction of movement or action.

i.e. <i>Please put the oranges into the box.</i>

There is more, but this is a simple explanation. I hope it helps.

How about "on" Vs. "onto" EFL_Geek?
Please explain.

Same rules apply. "Onto" is a preposition, you only use "on to" if one of the words is not a preposition i.e. part of a predicate/infinitive.

I speak perfect English and that is one of those things that native speakers just know. EFL Geek is correct but I couldn't think of that myself.

> "Onto" is a preposition, you only use "on to"
> if one of the words is not a preposition i.e.
> part of a predicate/infinitive.

What about "I plan to continue on to graduate school"?