How to use in, into, and in to?

In, into and in to are one of the most confused structures in English grammar. In this post we will cover all the area of confusion regarding them.

When is "in" used in a sentence?

In can be a noun, a preposition, an adverb, an adjective, .
In means within or inside.
As a preposition, In is used for location and condition.

1. My mother is in house, and she is in a good condition.

If you use in as an adverb it shows movement.

1. Shen drinks coffee with milk in.
2. They went in when we visited.

  

When is "into" used in a sentence?

Into is used as a preposition; it shows movement and direction from outside to inside.

1. They are rushing into the house.
2. Come into my house.
3. He threw her wife into the fire.

Into is also used to show a change in state.

1. The frog turn into prince.
2. We translate the English into Hindi.

   

What about "in to" ?

In to is combined form of In as an adverb and to as a preposition or infinitive, like to see, to go, to run, to walk, etc. 

1. She went in to see her husband. (Here to is working as infinitive.)
2. The assistant takes the day's agenda in to the president. (Here to is preposition.)

What is the difference between "into" and "in"?

The foremost difference between into and in is that into shows movement, whereas in shows a position inside.

There is an exception.

Sometimes in also shows movement, when it is used as an adverb, for example "Soldiers opened the door and rushed in".

Here in works as an adverb suggesting that soldiers moved inside .
                                      Into works as a preposition only. Hence it demands a noun or pronoun after it to show a movement. If you write "He came into", this doesn't make any sense. You must include a noun or pronoun to show a movement. You should write "He came into the house"; here "house" is a noun, and you can observe a movement. Without noun "into" can't show any movement. However, this is not the case with "in" because "in" works as adverb also. If you say, "He came in", you don't need a noun or pronoun because here "in" is working as an adverb in this sentence.

What Good Word Guide says, 

As prepositions, into and in are occasionally interchangeable: He put the letter into/in his pocket. Into usually suggests movement from the outside to the inside, whereas in suggests being or remaining inside. In many contexts the two prepositions are not interchangeable: They sailed into the harbour at four o'clock. They sailed in the harbour all afternoon.

What do you mean by "In toto"?

In toto, the Latin phrase, means completely, entirly, including all parts.

1. They agreed in toto.
2. Company accepted the proposal in toto.

Some other usages of Into:
If you talk someone into doing something, you persuade them to do it.

1. My mother tried to talk me into getting married.

If you are very interested in something and like it very much, you  can say that you are into it.

1. I am into writing.
2. Husband should be into his wife.
3. Sons are into their mother.

Common Errors:

The radio was tuned into the BBC World Service.  ✘
The radio was tuned in to the BBC World Service.  ✔

Tune something in to something means to adjust the controls on a radio or television on a radio or television so that you can receive a particular programmer or channel.

You need password to log into our website.   ✘
You need password to log in to our website.   ✔
   Long in/on means to perform the action that allow you to begin using a computer system

In a nutshell
In is used for position, whereas into is for a movement from outside to inside.
In is also used for movement if it works as an adverb.
In to is the combination of in as an adverb and to, preposition, or a part of an infinitive. 

Source:-  Good Word Guide: The fast way to correct English - spelling, punctuation, grammar and usage

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