“into” vs. “in to”
Write "into" as one word for movement toward an interior or a change of state; write "in to" as two words whenever "in" belongs to a phrasal verb that's simply followed by a separate "to" phrase.
into
"Into" is a single preposition showing movement toward the inside of something, or a change of state ("walk into the room," "turn water into ice"). "Into" formed in Middle English by fusing the two older separate words "in" and "to" into one preposition specifically to express directional movement, distinguishing it from the static, no-motion sense that plain "in" alone continued to carry.
in to
"In to," written as two separate words, occurs when "in" (part of a phrasal verb like "turn in," "log in," "drop in") happens to be followed immediately by the separate preposition "to," purely by coincidence of sentence structure ("she went in to see the doctor," where "went in" is one idea and "to see the doctor" explains why). There's no single combined word here at all — it's simply two ordinary, unrelated words that happen to land next to each other.
The real distinction
The key test is whether "in" is actually part of a phrasal verb (a two-word verb whose meaning depends on both words together, like "turn in," "check in," "give in") immediately followed by an unrelated "to." If removing "to" and everything after it still leaves a complete, sensible phrasal verb ("she turned in" still makes sense on its own), you likely need the two-word "in to"; if the sentence needs "into" as a single unit describing motion toward an interior or a transformation, no such phrasal verb is present. Compare "she turned into a great leader" (single preposition "into," describing transformation — there's no phrasal verb "turn into" being split apart) against "she turned in to the front desk" (phrasal verb "turn in" meaning "submit" or "report," followed by the separate preposition "to" introducing a destination). This is a genuinely less common error than most homophone confusions on this site because "in to" and "into" aren't even pronounced identically in careful speech — "into" typically gets a single, blended stress, while "in to" retains two separate stressed syllables — but the error still shows up regularly in fast or informal writing where a writer isn't parsing the phrasal-verb structure consciously. Editors specifically watch for this error after common phrasal verbs like "log in," "turn in," "hand in," "drop in," and "check in," since all five are frequently followed by a "to" phrase that a fast typist may fuse into a single incorrect "into."
Examples with “into”
- The kids ran into the house when it started raining.
- She poured the batter into the pan.
- The caterpillar transformed into a butterfly.
- He walked into the wrong meeting by mistake.
- The negotiations turned into a shouting match.
- We're heading into a busy season at work.
- The car crashed into a parked truck.
- Their small business grew into a national brand.
Examples with “in to”
- She went in to see the doctor about her cough.
- He turned his badge in to security before leaving.
- They dropped in to say a quick hello.
- Please hand your assignment in to the front desk.
- He checked in to confirm his flight was on time.
- She came in to grab her forgotten umbrella.
- We called in to report the missing package.
- He logged in to check his account balance.
Memory trick
Ask whether "in" could stand alone as half of a familiar two-word verb (turn in, log in, check in, hand in) with "to" just tagging along afterward to introduce a destination or reason — if so, keep them as two separate words. If instead the sentence is describing motion straight toward the inside of something, or one thing changing into another, fuse them into the single word "into." One more useful check: try reading the sentence with a brief pause between "in" and "to" — if that pause sounds natural, they're two separate words; if the phrase wants to be read as one smooth unit, it's the single preposition "into."