Of arts, some are demonstrable, others indemonstrable; and demonstrable
are those the construction of the subject whereof is in the power
of the artist himself, who, in his demonstration, does no more
but deduce the consequences of his own operation... Geometry
therefore is demonstrable, for the lines and figures from which we
reason are drawn and described by ourselves; and civil philosophy is
demonstrable, because we make the commonwealth ourselves. But
because of natural bodies we know not the construction, but seek it
from the effects, there lies no demonstration of what the causes be we
seek for, but only of what they may be.