What is what part of speech is to?

The word "to" can function as several different parts of speech, most commonly as a preposition or as an infinitive marker.

• Preposition: As a preposition, "to" expresses direction, location, or a relationship. It's followed by a noun or pronoun (the object of the preposition). For example, "I went to the store" or "Give it to me."

• Infinitive Marker: "To" is used before the base form of a verb to form the infinitive form. For example, "I want to eat." In this case, "to eat" is the infinitive form of the verb "eat."

Less frequently, "to" can also function as an adverb, though this usage is relatively uncommon.