Fallacies of Division

In one line

Each fallacy of division is the breach of one of the five rules, and each has a name.

In the wording a student can write in an examination: the fallacies of division are cross-division, where more than one principle is used at once; overlapping division, where the subclasses are not mutually exclusive; division that is not exhaustive, and division that is too wide; division by leaps; and the substitution of partition for division.

Cross-division

The rule broken. One fundamentum divisionis at a time.

The fallacy. Two or more principles applied in one division, so that the resulting classes belong to different schemes.

The plain example. Books divided into paperbacks, hardbacks and dictionaries. Two principles, binding and subject matter, and a hardback dictionary belongs in two places at once.

The legal example, and it is common. Suits divided into money suits, suits for possession and suits filed in forma pauperis. The third is a division by the manner of filing and the first two by the relief claimed, so a pauper's suit for money falls in two classes and there is no way to tell how many kinds of suit the scheme recognises.

Why it is dangerous rather than merely untidy. A cross-division makes both of the other defects invisible. Once two principles are running, an overlap looks like an accident and a gap cannot be found at all, because there is no single attribute whose presence or absence can be checked.

Overlapping division

The rule broken. The membra dividentia must be mutually exclusive.

The fallacy. A member of the genus falls into two subclasses although only one principle is in use.

How it happens with a single principle. Where the fundamentum is a matter of degree rather than of presence or absence. Dividing injuries into slight, serious and grievous uses one principle, severity, and produces overlaps at every boundary because the words are vague and their ranges are not marked off.

The legal consequence. Two provisions apply to one case and they may prescribe different things. A drafter who divides by degree has to fix the boundaries numerically, or by reference to a defined test, or accept that the classes will be argued about.

Division that is not exhaustive

The rule broken. The subclasses together must equal the genus.

The fallacy. Something in the class falls into no subclass.

Examples. Courts divided into civil and criminal, omitting the tribunals and the revenue courts. Decrees divided into preliminary and final, omitting a decree that is partly one and partly the other. Evidence divided into oral and documentary, omitting, on the older view, the material object produced for inspection.

The legal consequence is a gap, and a gap in a statutory division is a case the Act does not reach. It cannot be cured by construction, since reading a class wider than its words is the error material obversion produces at sequence 500; it is cured by amendment.