To

To is one of the most common words in English, serving several distinct grammatical roles. Etymologically, it comes from Old English tō, from Proto-Germanic *tō, and ultimately from a Proto-Indo-European root meaning toward or in the direction of. In modern usage, it appears most often as a preposition and as the infinitive marker for verbs.

As a preposition, to marks direction, destination, or contact with a person or thing. Examples include go to the store, send a letter to John, and translate from English to Spanish. It also expresses the limit or extent of something, as in from ten to twenty, or prices ranging from five to ten dollars. In addition, to can indicate purpose or intention in phrases like a key to success or steps to follow. It is also used in various fixed expressions and idioms.

As the infinitive marker, to accompanies a verb to form the infinitive, as in to eat, to be, or to run. This use is central to English verb morphology, though after certain auxiliary verbs or in some subordinate clauses the infinitive is omitted or altered (for example, must go, would like to go). The to-infinitive differs from the gerund or present participle in form and function.

Pronunciation varies by context and emphasis. It is typically pronounced /tə/ in unstressed positions and /tuː/ when stressed or carefully enunciated. Common pitfalls include confusion with the homophones two and too, which have unrelated meanings and spellings.