in, into

In has a basic meaning of "within a space or a place": "The family was sitting in the room." As distinguished from in, into indicates movement or direction to an interior location. Say "Molly was in the kitchen" and "Molly walked into the kitchen." If you pause between in and to (say in to rather than into), in becomes an adverb: "You may now go in to see the new baby." In is an indispensable word, but perhaps one does not have to use it so often in such trite expressions as "have it in for" ("hold a grudge"),"ins and outs" ("twists and turns," "changing conditions"),"all in" ("fatigued"),"in for" ("guaranteed," "about to receive"),"in that" ("since"),"have an in" ("possess access or favor"),"in group" ("incumbent or favored group"),"in with" ("on friendly terms"),"in apple-pie order," "in black and white," "in the last analysis," "in the same boat," and "in spite of the fact that" and in a rash of new terms such as laugh-in, teach-in, talk-in, sit-in, be-in.