The trouble with attempting to apply formal logic systems to
  humans is that they are incompatible systems. Cognitively, the
  amygdala puts the emotional "push" into the pre-frontal cortex
  at a greater speed and "width of the pipe" (physical analogy)
  than the pathway going from the pre-frontal cortex back to the
  amygdala. Emotions come before logic most of the time. To expect
  humans to follow formal logic systems in their life choices is
  not logical. Also, certainty is an emotional state codified as
  "truth" in logic systems. The systems are from humans, based
  upon our limited understanding of the cognitive systems as they
  existed at the time of the formulation of the logic systems and
  then carried on utilizing their own rules once removed from our
  misunderstanding of human cognitive systems. Unless you believe
  in a platonic realm where such things as formal logic exist in
  an permanent state that we can draw from and never changes. But
  that's just silly. == was getting tired of the continual appeal
  to formal logic as if it's a system that really matters for
  anything except conversational games, at least in how I've seen
  it used. ==