if' means
'whenever' or 'all cases in which'; for to raise a doubt whether a
straight line is ever conceived to fall upon another, whether bodies are
ever unsupported, or population ever increases, is a superfluity of
scepticism; and plainly the hypothetical form has nothing to do with the
proof of such propositions, nor with inference from them.

Still, the disjunctive form is necessary in setting out the relation of
contradictory terms, and in stating a Division (chap. xxi.), whether
formal (_as A is B or not-B_) or material (as _Cats are white, or black,
or tortoiseshell, or tabby_). And in some cases the hypothetical form is
useful. One of these occurs where it is important to draw attention to
the condition, as something doubtful or especially requiring
examination. _If there is a resisting medium in space, the earth will
fall into the sun; If the Corn Laws are to be re-enacted, we had better
sell railways and buy land_: here the hypothetical form draws attention
to the questions whether there is a resisting medium in space, whether
the Corn Laws are likely to be re-enacted; but as to methods of
inference and proof, the hypothetical form has nothing to do with them.
The propositions predicate causation: _A resisting medium in space is a
condition of the earth's falling into the sun; A Corn Law is a condition
of the rise of rents, and of the fall of railway profits_.

A second case in which the hypothetical is a specially appropriate form
of statement occurs where a proposition relates to a particular matter
and to future time, as _If there be a storm to-morrow, we shall miss our
picnic_. Such cases are of very slight logical interest. It is as
exercises in formal thinking that hypotheticals are of most value;
inasmuch as many people find them more difficult than categoricals to
manipulate.

In discussing Conditional Propositions, the conditional sentence of a
Hypothetical, or the first alternative of a Disjunctive, is called the
Antecedent; the indicative sentence of a Hypothetical, or the second
alternative of a Disjunctive, is called the Consequent.

Hypotheticals, like Categoricals, have been classed according to
Quantity and Quality. Premising that the quantity of a Hypothetical
depends on the quantity of its Antecedent (which determines its
limitation), whilst its quality depends on the quality of its consequent
(which makes the predication), we may exhibit four forms:

A. _If A is B, C is D;_
I.