What's the difference between “ti” and “te”?

Question

I've heard both "ti" and "te" in learning Spanish, and I don't understand the difference.

"Ti" I've heard in:

¿Y a ti?

and "te" I've heard in

¿Te gusta ___?

So what's the difference in how they're used? Why isn't it "y a te" or "ti gusta _"?

Answer 1

An edifying answer from Pablo, but I want to help the OP understand the pattern and develop some intuition for the difference.

Why isn't it "Y a te" and "¿Ti gusta el saco azul?"?

Te is a very unstressed word, kind of like "a" (indefinite article) in English. For example, "I could eat a horse": notice that "a" has the smallest amount of stress of all the syllables in the sentence. In the pronunciation of "te", we have an analogous situation. Imagine two polite people surpassing each other in their polite thanking: "Thank you." "Thank you." "No, really, it is you who have gone out of your way to help me etc." And now in Spanish: "Gracias." "Gracias a ti." Etc.

In "¿Te gusta el saco azul?" the "te" is an unstressed word. The most stressed word in this sentence is "azul," and "te" does not get much stress. "Ti" wouldn't fit here because "ti" is a stressed word.

If you want to show emphasis, for example, "I know that you like the blue jacket better, but my boss wants me to wear the black one": "Sé que a ti te gusta más el saco azul, pero mi jefe quiere que use el negro." I'm using italics for "ti" here so you'll notice how I spelled it, and also to indicate the intonation. "Ti" here is quite stressed, and this indicates the contrast.

In short, "ti" works more comfortably in a stressed pronunciation, and "te" is more of a throwaway word (in terms of pronunciation).

Answer 2

Ti and te are both second person singular pronouns, the equivalent of English singular you in object position. The difference has to do with emphasis.

Te is the non-emphatic pronoun. It is clitic, i. e. it appears always phonetically attached to another word (in this case, a verb). As with other non-emphatic pronouns, it may go either before or after the verb, depending on certain rules. If it goes before, it is written separately; if after, it is written together with the verb.

Te vi esta mañana pero no pude hablarte.
"I saw you this morning but I couldn't talk to you."

Ti is the emphatic form of the second person singular pronoun. It is not a clitic, so it has its own stress; it is not attached to other words. It is used after prepositions. Note that in Spanish the direct object of a verb, if it refers to a person, requires the preposition a, so you will find this emphatic form a lot in those cases.

Para esta tarea te elijo a ti.
"For this task I choose you."

As above, you will sometimes find both ti and te in the same sentence, referring to the same person, when they are the object of a verb. You cannot say Yo elijo a ti (without te); it's ungrammatical. You will find ti on its own when it is not the verb object:

Traje esto para ti.
"I brought this for you."

The above works the same for me and mí (first person singular), except that the emphatic pronouns are actually written together with the preposition con and they change form: conmigo, contigo. The rest of the pronouns do not have special emphatic forms (the same forms are used as in the subject position).