expected in letters or essays, nor that exactness of method, nor that fulness of the several parts which they affect to observe who presume to write philosophical treatises.  The merit of brevity is relative to the manner and style in which any subject is treated, as well as to the nature of it; for the same subject may be sometimes treated very differently, and yet very properly, in both these respects.  Should the poet make syllogisms in verse, or pursue a long process of reasoning in the didactic style, he would be sure to tire his reader on the whole, like Lucretius, though he reasoned better than the Roman, and put into some parts of his work the same poetical fire.  He may write, as you have begun to do, on philosophical subjects, but he must write in his own character.  He must contract, he may shadow, he has a right to omit whatever will not be cast in the poetic mould; and when he cannot instruct, he may hope to please.  But the philosopher has no such privileges.  He may contract sometimes, he must never shadow.  He must be limited by his matter, lest he should grow whimsical, and by the parts of it which he understands best, lest he should grow obscure.  But these parts he must develop fully, and he has no right to omit anything that may serve the purpose of truth, whether it please or not.  As it would be disingenuous to sacrifice truth to popularity, so it is trifling to appeal to the reason and experience of mankind, as every philosophical writer does, or must be understood to do, and then to talk, like Plato and his ancient and modern disciples, to the imagination only.  There is no need, however, to banish eloquence out of philosophy, and truth and reason are no enemies to the purity nor to the ornaments of language.  But as the want of an exact determination of ideas and of an exact precision in the use of words is inexcusable in a philosopher, he must preserve them, even at the expense of style.  In short, it seems to me that the business of the philosopher is to dilate, if I may borrow this word from Tully, to press, to prove, to convince; and that of the poet to hint, to touch his subject with short and spirited strokes, to warm the affections, and to speak to the heart.

Though I seem to prepare an apology for prolixity even in writing essays, I will endeavour not to be tedious, and this endeavour may succeed the better perhaps by declining any over-strict observation of method.  There are certain points of that which I esteem the first philosophy whereof I shall never lose sight, but this will be very consistent with a sort of epistolary licence.  To digress and to ramble are different things, and he who knows the country through which he travels may venture out of the highroad, because he is sure of finding his way back to it again.  Thus the several matters that may arise even accidentally before me will have some share in guiding my pen.