He starts his paper from 1987  with a reference to the PROSPECTOR expert system which was using Bayes rules to handle uncertain knowledge. Then he explains the idea behind probabilistic logic which is used for determine the value of true/false statements in a semantic tree. The probability values are displayed in a 3d box graphically to make the concept clearer for the newbies. He calls the concept
quote: “straightforward generalization of the ordinary true-false semantics”
But something is wrong with the paper. Approximately in the middle of the text, i missed the point why such an alternative logic concept is useful. Isn't it enough to deal with normal yes/no statements which can stored in a Turing machine much easier? Why do we need complicated 3d boxes with a probability landscape?
 Nilsson, Nils J. "Probabilistic logic." Artificial intelligence 28.1 (1986): 71-87.