He has trouble processing your grammar and syntax. I am not always sure about exactly what you mean, either. I am sorry. That's not a criticism, and it's not meant to be hurtful. it's just a statement of fact.
If I recall correctly, Lucas doesn't know ASL, and as I have mentioned before, I seem to have a serious learning block when it comes to 'getting' the grammar.
I'm trying. But I have a long way to go.