After the first measure, the second half of the measure should contain a
consonance (Fig. 63_a_), the first half a consonance (_b_), or dissonance
(_c_), preferably the latter, in which case a suspension is formed. This is
the most desirable form of syncopation. When the first half contains a
dissonance, the counterpoint must descend--or ascend in retardation
(_d_)--one degree to an imperfect consonance (_c_). When the first half is
a consonance, it may be left by a skip to some other chord-tone (_e_), or
by degreewise progression (_f_). In the latter case the second note is
non-harmonic, and therefore should not be used to prepare a syncopation
except as in Fig. 63_d_ (Retardation of the root in I_6).

[Illustration: Fig. 63.]

When writing three notes to one in the fourth species, the suspension may
resolve on the second beat (_a_), or the third (_b_). In the latter case,
the suspension skips (_c_) to some other chord-tone, before resolving. The
resolution to the leading-tone (_d_) forms an important exception to this
rule. [Fig. 64.]

[Illustration: Fig. 64.]

The fifth may be used in the lower part if it becomes the preparation of a
suspension (Fig. 65_a_). It may also be used in the lower part, as in Fig.
65_b_, provided it resolves by skipping to the third of the chord.

In skipping from the fifth to the root, or the reverse, in the lower part,
do so in an upward direction. The fifth, when treated as an harmonic
passing-tone, may, however, be approached either ascending or descending.