HHDL wrote:"The essential point is this: The luminous and knowing aspect of a given state of consciousness must come from a prior moment of that consciousness. It follows, therefore, that it must also beginningless. For were a beginning to the continuum of the luminous and knowing aspect of consciousness posited, we would then have to concede that consciousness arose from a cause that is not commensurate with it, which is untenable. "
And I have gone back and reread it. Suddenly something jumped out at me. I think I made an error in understanding what the subject matter was.
He did not say that consciousness arises from a previous moment, although that may be true. He said the luminous and knowing aspect arises from a prior moment of consciousness, and that is the subject of the paragraph, not consciousness itself.
This could change the discussion completely.
There has been some wrestling here about the mention of commensurate causes. I don't know much about the idea, but I believe that it basically means a virtuous action will not give rise to bad karma, and an apple will not give rise to a rhinoceros. There is a limit to what may arise from a given cause, and in some sense the effects carry forward some of the characteristics of their causes.
Now I need to sort out the logical consequences of all this. I'm pretty sure that when he used the phrase "The essential point is this" he was implying that what followed was a condensation that omitted extensive supportive reasoning for the sake of brevity.
Now I feel like I am getting somewhere. Maybe only a single step forward, but hey I'm not a sprinter.