Beattie's Essay on Truth, Part I, Chapter 2, is a long section
devoted to giving an inductive argument for the position that
all human inquiry, and thus all knowledge, is based on first
principles. In order to show that his induction is reasonably
comprehensive, he runs through the basic ideas underlying his
various categories in an interesting footnote. All the objects
of understanding, i.e,. things we can genuinely be said to know
in some way, are either abstract ideas and relations or things
that really exist. If we are speaking of abstract ideas, we are
in the realm of mathematical evidence, which consists either of
immediate intuitive evidence or the evidence of strict
demonstration. If we are talking about what really exists,
knowledge is experiential in some way, and we are either talking
about our own experiences or someone else's. If we are talking
about our own experiences, then we are either talking certainty
or probability. If certainty, this pertains to the evidence of
external senses, the eviden