nce,
or point of repose; the first--called the _Antecedent phrase_--has its
cadence in the fourth measure, and the second--called the _Consequent
phrase_--in the eighth measure. The effect of the Period-form is that
of a longer sentence interrupted exactly in the middle,--not unlike a
bridge of two spans, resting on a central pier. But, precisely as the
central pier is only an intermediate point of support, and not terra
firma, so the ending of the Antecedent phrase is never anything more
weighty than a semicadence, while the definite, conclusive, perfect
cadence appears at the end of the Consequent phrase,--or of the entire
period-form.

The reason for this distinction of cadence is obvious. A period is not
two separate phrases, but two related and coherent phrases which
mutually balance each other. The Consequent phrase is not merely an
"addition" to the first, but is its complement and "fulfilment." The
two phrases represent the musical analogy of what, in rhetoric, would
be called thesis and antithesis, or, simply, question and answer. In a
well-constructed period the Antecedent phrase is, therefore, always
more or less _interrogative_, and the Consequent phrase _responsive_,
in character.

For illustration (Mendelssohn, No. 28):--

[Illustration: Example 44. Fragment of Mendelssohn.]

The co-operation, or interaction, of the principles of Unity and
Variety, is nowhere more strikingly shown than in the formulation of
the musical period. Either element has the right to predominate, to a
reasonable degree, though never to the exclusion or injury of the
other. In the above example, the principle of Unity predominates to a
somewhat unusual extent:--not only the figures (marked 1-2-3-4), and
the motives (_a-b_), are uniform, in the Antecedent phrase itself, but
the melody of the Consequent phrase corresponds very closely throughout
to that of the Antecedent, only excepting a trifling change in the
course (marked _N. B._), and the last few tones, which are necessarily
so altered as to transform the semicadence into a perfect cadence. It
is this significant change, _at the cadence_, which prevents the second
phrase from being merely a "repetition" of the first one,--which makes
it a "Consequent," a response to the one that precedes.

Further (Mendelssohn, No. 23):--

[Illustration: Example 45. Fragment of Mendelssohn.]

In this example also, the Consequent phrase is a complete affirmation
of its Ant