The chord most frequently used in modulating is the dominant seventh, i.e., a seventh chord (see [Sec. 201]) on the dominant tone of the key. In the key of C this chord is G—B—D—F; in the key of D it is A—C♯—E—G; in the key of A♭ it is E♭—G—B♭—D♭, etc.
210. A suspension is the temporary substitution of a tone a degree higher than the regular chord-tone, this temporary tone being later replaced by the regular chord-tone. See Fig. 76 (a).
211. A retardation is the temporary substitution of a tone a degree lower than the regular tone, this tone (as in the case of the suspension) being later replaced by the regular chord tone. See Fig. 77 (a).