Michael Scriven further developed the Beardsley-Thomas approach in his 1976 book "Reasoning". Whereas Beardsley had said "At first, write out the statements...after a little practice, refer to the statements by number alone" Scriven advocated clarifying the meaning of the statements, listing them and then using a tree diagram with numbers to display the structure. Missing premises (unstated assumptions) were to be included and indicated with an alphabetical letter instead of a number to mark them off from the explicit statements. Scriven introduced counterarguments in his diagrams, which Toulmin had defined as rebuttal. This also enabled the diagramming of "balance of consideration" arguments.