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Common Errors in English Usage Dictionary
INTO & IN TO
“Into” is a preposition
which often answers the question, “where?”
“Tom and Becky had gone far into the cave
before they realized they were lost.”
Sometimes the “where” is metaphorical,
as in, “He went into the army” or
“She went into business.”
It can also refer by analogy to time:
“The snow lingered on the ground well into April.”
In old-fashioned math talk,
it could be used to refer to division:
"Two into six is three.”
In other instances where the words “in” and “to”
just happen to find themselves neighbors,
they must remain separate words.
“Rachel dived back in to rescue the struggling boy.”
Here “to” belongs with “rescue”
and means “in order to,” not “where.”
(If the phrase had been “dived back into the water,”
“into” would be required.)
Try speaking the sentence concerned aloud,
pausing distinctly between “in” and “to.”
If the result sounds wrong, you probably need “into.”
Then there is the 60s colloquialism
which lingers on
in which “into” means
“deeply interested or involved in”:
“Kevin is into baseball cards.”
This is derived from usages like
“the committee is looking into the fund-raising scandal.”
The abbreviated form is not acceptable formal English,
but is quite common in informal communications.
Collins COBUILD English Usage
The preposition into is
usually used with verbs of movement.
You use into to say where someone or something goes,
or where something is put.
I went into the yard.
He poured tea into the cup.
After verbs meaning put, throw, drop, or fall,
you can use into or in with the same meaning.
Chen put the letter into his pocket.
She put the key in her purse.
He fell into a pond.
One of the boys fell in the river.
Before here and there, use in, not 'into'.
Come in here.
Put your bags in there.