The Period
The Period-form is obtained by the addition of a second
phrase to the first. It is therefore, in a sense, a double phrase;
that is, it consists of two connected phrases, covering eight ordinary
measures, or just double the number commonly assigned to the single
phrase.
Each one of these phrases must, of course, have its individual cadence,
or point of repose; the first--called the Antecedent phrase--has
ts
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):--
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):--
In this example also, the Consequent phrase is a complete affirmation
of its Antecedent, agreeing in its melodic form with the latter until
the cadence is nearly due, when an extra measure is inserted (as
extension), and the usual digression into the necessary perfect cadence
is made. The condition of Unity predominates, but a noticeable
infusion of Variety takes place.
Further (Mozart, pianoforte sonata):--
Here, again, the condition of Unity prevails, but with a still greater
infusion of Variety; the melody of the Consequent phrase resembles
that of the Antecedent in every detail; the rhythm is identical, and it
is evident that the second phrase is designed to balance the first,
figure for figure, the principal change being that some of the figures
are simply turned upside down (compare the places marked N. B.). The
semicadence rests upon a dominant chord (fifth-step) of D major; the
perfect cadence upon the same chord, it is true, but as tonic harmony
of A major, with keynote in the extreme parts. Being a keynote, though
not in the original key, it is valid as perfect cadence.
Further (Beethoven, pianoforte sonata, op. 13):--
In this example, the condition of Variety predominates decidedly. The
Consequent melody differs totally from the Antecedent, even in rhythm,
and the necessary portion of Unity is exhibited only in equality of
length, uniformity of accompaniment, and similarity of character
(tonality, and general harmonic and rhythmic effect). Observe the
diversity of melodic extent, in the two phrases, in consequence of the
preliminary tone borrowed from the semicadence for the Consequent
phrase. Greater variety than here will rarely be found between two
successive phrases that are intended to form the halves of one coherent
period.
For more minute technical details see the HOMOPHONIC FORMS, Chapter V.