Some words there are which I cannot explain, because I do not understand them; these might have been omitted very often with little inconvenience, but I would not so far indulge my vanity as to decline this confession: for when Tully owns himself ignorant whether lessus, in the twelve tables, means a funeral song, or mourning garment; and Aristotle doubts whether [word in Greek] in the Iliad, signifies a mule, or muleteer, I may surely, without shame, leave some obscurities to happier industry, or future information. The rigour of interpretative lexicography requires that the explanation, and the word explained, should always be reciprocal; this I have always endeavoured, but could not always attain. Words are seldom exactly synonimous; a new term was not introduced, but because the former was thought inadequate: names, therefore, have often many ideas, but few ideas have many names. It was then necessary to use the proximate word, for the deficiency of single terms can very seldom be supplied by circumlocution; nor is the inconvenience great of such mutilated interpretations, because the sense may easily be collected entire from the examples. In every word of extensive use, it was requisite to mark the progress of its meaning, and show by what gradations of intermediate sense it has passed from its primitive to its remote and accidental signification; so that every foregoing explanation should tend to that which follows, and the series be regularly concatenated from the first notion to the last. This is specious, but not always practicable; kindred senses may be so interwoven, that the perplexity cannot be disentangled, nor any reason be assigned why one should be ranged before the other. When the radical idea branches out into parallel ramifications, how can a consecutive series be formed of senses in their nature collateral? The shades of meaning sometimes pass imperceptibly into each other; so that though on one side they apparently differ, yet it is impossible to mark the point of contact. Ideas of the same race, though not exactly alike, are sometimes so little different, that no words can express the dissimilitude, though the mind easily perceives it, when they are exhibited together; and sometimes there is such a confusion of acceptations, that discernment is wearied, and distinction puzzled, and perseverance herself hurries to an end, by crouding together what she cannot separate. These complaints of difficulty will, by those that have never considered words beyond their popular use, be thought only the jargon of a man willing to magnify his labours, and procure veneration to his studies by involution and obscurity. But every art is obscure to those that have not learned it: this uncertainty of terms, and commixture of ideas, is well known to those who have joined philosophy with grammar; and if I have not expressed them very clearly, it must be remembered that I am speaking of that which words are insufficient to explain.