This chapter is an attempt to put our ideas of offences into an exact method. The particular uses of method are various: but the general one is, to enable men to understand the things that are the subjects of it. To understand a thing, is to be acquainted with its qualities or properties. Of these properties, some are common to it with other things; the rest, peculiar. But the qualities which are peculiar to any one sort of thing are few indeed, in comparison with those which are common to it with other things. To make it known in respect of its difference, would therefore be doing little, unless it were made known also by its genus. To understand it perfectly, a man must therefore be informed of the points in which it agrees as well as of those in which it disagrees, with all other things. When a number of objects, composing a logical whole, are to be considered together all of these possessing with respect to one another a certain congruency or agreement denoted by a certain name, there is but one way of giving a perfect knowledge of their nature; and that is, by distributing them into a system of parcels, each of them a part, either of some other parcel, or, at any rate, of the common whole. This can only be done in the way of bipartition, dividing each superior branch into two, and but two, immediately subordinate ones; beginning with the logical whole, dividing that into two parts, then each of those parts into two others; and so on. These first-distinguished parts agree in respect of those properties which belong to the whole: they differ in respect of those properties which are peculiar to each. To divide the whole into more than two parcels at once, for example into three, would not answer the purpose; for, in fact, it is but two objects that the mind can compare together exactly at the same time. Thus then, let us endeavour to deal with offences; or rather, strictly speaking, with acts which possess such properties as seem to indicate them fit to be constituted offences. The task is arduous, and as yet at least, perhaps for ever, above our force. There is no speaking of objects but by their names: but the business of giving them names has always been prior to the true and perfect knowledge of their natures. Objects the most dissimilar have been spoken of and treated as if their properties were the same. Objects the most similar have been spoken of and treated as if they had scarce anything in common. Whatever discoveries may be made concerning them, how different soever their congruencies and disagreements maybe found to be from those which are indicated by their names, it is not without the utmost difficulty that any means can be found out of expressing those discoveries by a conformable set of names. Change the import of the old names, and you are in perpetual danger of being misunderstood: introduce an entire new set of names, and you are sure not to be understood at all. Complete success then, is, as yet at least, unattainable. But an attempt, though imperfect, may have its use: and, at the worst, it may accelerate the arrival of that perfect system, the possession of which will be the happiness of some maturer age. Gross ignorance descries no difficulties; imperfect knowledge finds them out, and struggles with them: it must be perfect knowledge that overcomes them.

IPML Chapter 16 Section 1