This may concern the validity of a deductive argument
(and, when coupled with validity, we may ask why the premises are true (or false), which has to do with the soundness of the argument); or, it may concern the strength of an inductive argument (and, when coupled with strength, we may ask why the premises are true (or false), which has to do with the cogency of the argument).
He does not explain what, exactly, deduction is, but we may say that a valid deductive argument
is an argument in which the premises entail the conclusion: If the premises are true, then the conclusion must be true.
I try not to have a linear, deductive argument
but rather these quite short, poemlike concepts--what Walter Benjamin called the Gedankenbild, or the "idea-image.
The book's flaws consist primarily of an inductive rather than deductive argument
about nurturing, faith, and a rather startling lack of detail in its citations.
A deductive argument
takes the same form as a mathematical equation.