The rigour of interpretative lexicography requires that the explanation, and the word explained, should be always reciprocal; this I have always endeavoured, but could not always attain.  Words are seldom exactly synonymous; 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 crowding 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.

The original sense of words is often driven out of use by their metaphorical acceptations, yet must be inserted for the sake of a regular origination.  Thus I know not whether ardour is used for material heat, or whether flagrant, in English, ever signifies the same with burning; yet such are the primitive ideas of these words, which are, therefore, set first, though without examples, that the figurative senses may be commodiously deduced.