When should I use the word 'yo' in a sentence where the verb conjugation already shows that I am the subject?

Question

Early on while I was learning Spanish, my teachers would always make us use the pronoun 'yo' even if it was redundant:> Yo pienso que... > Yo quiero... > Yo hablo... > etc.However, a more advanced Spanish book I bought told me only to use redundant pronouns like yo when I wanted to emphasize that ***I*** was performing the action (and when clarification of the subject was necessary). When should I use 'yo' in my sentences in Spanish? Does it make me sound rather self centered if I use it constantly? How and when do native speakers use it?

Answer 1

Yo can be used to emphasize that you are/are not the subject of the sentence:

¿Quién rompió el florero? --¡No fui yo!

Yo might be used to clarify or distinguish between several subjects in the sentence.

Yo andaba mientras que ella corría.

Answer 2

In Spanish if you are already speaking about yourself it sounds more appropriate to say > Pienso que...

Yo pienso < you would use in a conversation were you are specifying that, say: "well you had your turn to talk, I THINK this other thing about X subject.

However; if you visit a spanish speaking country the difference between adding <Yo> to your sentences or not, will not make too much of a difference.. A lot of Spanish speaking people use <Yo> too much.

Both, Pienso que and Yo Pienso que are acceptable.

It should only sound reduntant if you use the actual YO word more than once in a sentence.

Recap: Both ways are correct. The sentence without the word YO simply sounds better/ less informal.