You may end a sentence with a preposition!

It's a common misconception that you should never end a sentence with a preposition. Many grammarians argue that it's perfectly okay to do so, if the case warrants it.

What is a preposition?

A preposition, and the prepositional phrase which contains it, describes a relationship between its object and the rest of the sentence. For example:

The horse is in the stable.
He went inside the house.
The students were very disrespectful toward their teacher.

For a more detailed description of prepositions

When it's okay to end a sentence in a preposition:

Take the following sentence for example:

Who did you talk to?

Try removing the preposition.

Who did you talk?

This doesn't make any sense, and the alternative, rewriting the sentence, sounds too awkward for every day use:

To whom did you talk?

Unless you're writing dialogue for a particularly pretentious character, it would not be a good idea to write this way.

When it's not okay:

On the other hand, if the preposition could be removed without changing the meaning of the sentence, then it should be.

E.g. There was nothing inside of the refrigerator, so they ordered pizza.

There was nothing inside the refrigerator, so they ordered a pizza.

E.g. Where are you going to?

Where are you going?

In each example the second sentence works better, both for brevity and clarity.

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Prepositions

A Preposition links nouns, pronouns, and phrases to other words in a sentence. The word or phrase that the preposition introduces is called the object of the preposition.

A preposition usually indicates the temporal, spatial or logical relationship of its object to the rest of the sentence as in the following examples:

The book is on the table.
The book is beneath the table.
The book is leaning against the table.
The book is beside the table.
She held the book over the table.
She read the book during class.

A prepositional phrase is made up of the preposition, its object and any associated adjectives or adverbs. A prepositional phrase can function as a noun, an adjective, or an adverb. The most common prepositions are "about," "above," "across," "after," "against," "along," "among," "around," "at," "before," "behind," "below," "beneath," "beside," "between," "beyond," "but," "by," "despite," "down," "during," "except," "for," "from," "in," "inside," "into," "like," "near," "of," "off," "on," "onto," "out," "outside," "over," "past," "since," "through," "throughout," "till," "to," "toward," "under," "underneath," "until," "up," "upon," "with," "within," and "without."

For example:

He was writing on an old, mechanical typewriter.

"on" is the preposition.

"on an old, mechanical typewriter" is the prepositional phrase.

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