Why Does Vader not think Yoda Has trained Luke?

"Anakin was actively using the Force to podrace when he was nine."

But not at that moment! So how did Qui-gon "sense" him?

 

The simplest answer is best: Vader believed Yoda to be dead.


Bit of speculation on my part, but I believe Palpatine will beat Yoda down in Ep. III with Anakin watching, proving to Anakin the power of the dark side, while causing both him AND Palpatine to believe Yoda to be dead.

 

A slightly different perspective. Vader could have assumed Yoda dead because neither he nor the Emperor had heard anything from the Master in decades but I think something else is a major reason for his naming of Obi-Wan in all matters concerning Luke.

Vader hates Obi-Wan. He blames everything that went wrong in his life on Obi-Wan. So it is only logical that Luke's strength (something that could be a stumbling block to his conversion to the Dark Side) would be blamed on Obi-Wan out of habit.

Vader's temper struck me when I was watching ANH: Special Edition today. In the beginning when he pissed, he speaks very harshly and seems awfully energetic (he moves pretty darn fast). I guess I never really noticed that before.

 

I agree with the above poster and with the person in another thread concerning Vader and Obi-Wan. Vader has Obi-Wan on his mind the entire trilogy. He is always saying 'something' about Obi-Wan (Obi-Wan has taught you well, Obi-Wan never told you what happened to your Father) even after he knows that Obi-Wan is dead. Because he probably thinks that Yoda is dead he assumes that Obi-Wan taught Luke everything.