such simple but explicit expressions as the above (_tertii adjacentis_).
A Compound Proposition, reducible to two or more simple ones, is said to
be exponible.

The modes of compounding sentences are explained in every grammar-book.
One of the commonest forms is the copulative, such as _Salt is both
savoury and wholesome_, equivalent to two simple propositions: _Salt is
savoury; Salt is wholesome. Pure water is neither sapid nor odorous_,
equivalent to _Water is not sapid; Water is not odorous_. Or, again,
_Tobacco is injurious, but not when used in moderation_, equivalent to
_Much tobacco is injurious; a little is not_.

Another form of Exponible is the Exceptive, as _Kladderadatsch is
published daily, except on week-days_, equivalent to _Kladderadatsch is
published on Sunday; it is not published any other day_. Still another
Exponible is the Exclusive, as _Only men use fire_, equivalent to _Men
are users of fire; No other animals are_. Exceptive and exclusive
sentences are, however, equivalent forms; for we may say,
_Kladderadatsch is published only on Sunday_; and _No animals use fire,
except men_.

There are other compound sentences that are not exponible, since, though
they contain two or more verbal clauses, the construction shows that
these are inseparable. Thus, _If cats are scarce, mice are plentiful_,
contains two verbal clauses; but _if cats are scarce_ is conditional,
not indicative; and _mice are plentiful_ is subject to the condition
that _cats are scarce_. Hence the whole sentence is called a Conditional
Proposition. For the various forms of Conditional Propositions see chap.
v. § 4.