necessary for all who would affect them upon solid and sure principles.  It is not enough to know them in general; to affect them after a delicate manner, or to judge properly of any work designed to affect them, we should know the exact boundaries of their several jurisdictions; we should pursue them through all their variety of operations, and pierce into the inmost, and what might appear inaccessible parts of our nature,

     Quod latet arcana non enarrabile fibra.

Without all this it is possible for a man, after a confused manner sometimes to satisfy his own mind of the truth of his work; but he can never have a certain determinate rule to go by, nor can he ever make his propositions sufficiently clear to others.  Poets, and orators, and painters, and those who cultivate other branches of the liberal arts, have, without this critical knowledge, succeeded well in their several provinces, and will succeed:  as among artificers there are many machines made and even invented without any exact knowledge of the principles they are governed by.  It is, I own, not uncommon to be wrong in theory, and right in practice:  and we are happy that it is so.  Men often act right from their feelings, who afterwards reason but ill on them from principle; but as it is impossible to avoid an attempt at such reasoning, and equally impossible to prevent its having some influence on our practice, surely it is worth taking some pains to have it just, and founded on the basis of sure experience.  We might expect that the artists themselves would have been our surest guides; but the artists have been too much occupied in the practice:  the philosophers have done little; and what they have done, was mostly with a view to their own schemes and systems; and as for those called critics, they have generally sought the rule of the arts in the wrong place; they sought it among poems, pictures, engravings, statues, and buildings.  But art can never give the rules that make an art.  This is, I believe, the reason why artists in general, and poets, principally, have been confined in so narrow a circle:  they have been rather imitators of one another than of nature; and this with so faithful an uniformity, and to so remote an antiquity, that it is hard to say who gave the first model.  Critics follow them, and therefore can do little as guides.  I can judge but poorly of anything, whilst I measure it by no other standard than itself.  The true standard of the arts is in every man’s power; and an easy observation of the most common, sometimes of the meanest things in nature, will give the truest lights, where the greatest sagacity and industry, that slights such observation, must leave us in the dark, or, what is worse, amuse and mislead us by false lights.  In an inquiry it is almost everything to be once in a right road.  I am satisfied I have done but little by these observations considered in themselves; and I never should have taken the pains to digest them, much less should I have ever ventured