text:  But if _all_ experience is in favour of a proposition--if no experience has occurred even to enable the imagination to conceive its opposite what more can be required to convert the general into a universal proposition? Strange to say the attribution of these characteristics of universality and necessity becomes amongst those who loudly insist upon the palpable nature of the distinction we are now examining a matter of controversy; and there are a class of scientific truths of which it is debated whether they are contingent or necessary