Trevor asks a lot of questions, and some time over the last year or so, we have explained the concept of gravity. He understands the concept.
He apparently also understands the concept of assessing blame.
The boys were in the basement on their own when Devin started to cry. It was an "I'm hurt" cry, instead of a "Trevor has what I want" cry. Daddy and I rushed down, and Daddy asked Trevor what happened. Trevor told Daddy that Devin fell. Daddy asked Trevor how it happened. Trevor explained that gravity made him fall. Daddy asked if he fell off the chair, and Trevor assured him that's exactly what happened...
just to make sure, when Trevor was out of earshot, I asked Devin if Trevor pushed him. Devin said, "yeh." To confirm, I said, "did you fall on your own?" Devin said, "yeh." I knew then that all was well.