Tú vs. ti
The Spanish words tú and ti both translate to the informal, singular you. The main difference between them lies in their grammatical function within a sentence. Tú is used as the subject, while ti is used after a preposition.
Tú
A1This is the subject pronoun for you. It is used to identify who is performing the action of the verb. A helpful tip is to remember that tú often comes before a conjugated verb.
Tú eres una persona muy amable.
(You are a very kind person.)
Ella es más inteligente que tú.
(She is more intelligent than you.)
Si tú no vas, yo tampoco voy.
(If you don't go, I'm not going either.)
Tú tienes la respuesta correcta.
(You have the correct answer.)
Ti
A1This is the prepositional object pronoun for you. It is always used after prepositions such as a, para, de, en, sin, or por. Ti is the receiver of the action or concept expressed by the preposition.
He comprado este libro para ti.
(I have bought this book for you.)
No puedo ir a la fiesta sin ti.
(I can't go to the party without you.)
Siempre están hablando de ti.
(They are always talking about you.)
A ti te encanta la música clásica.
(You love classical music.)
Tengo un mensaje importante para ti.
(I have an important message for you.)
Confío plenamente en ti.
(I trust you completely.)
Summary
In short, use tú as the subject who performs an action (Tú cocinas - You cook). Use ti after any preposition, like para, de, a, or sin (para ti - for you). A simple memory aid: tú has an accent mark, but ti never does.