On Imitation

A Theme is proposed in four parts, in one of the two choirs; the response should be made by the other choir.

In order that the response may be inverse:

• the bass of the Theme must be placed in the soprano part of the response,
• the soprano part must be placed in the bass,
• the alto part placed in that of the tenor, and
• lastly, that of the tenor, in the alto.

In order that the response may be contrary, each part of the response must respond by contrary movement, and in the order stated above, to the parts which have proposed the Theme.

In composing this device, the following rule must be observed: no one of the lower parts must ever form a fourth with the soprano, unless this fourth proceed by degree as a passing tone. With regard to contrary movement, it must be obtained by means of the scales mentioned in the second section, when this contrary movement was under discussion; for the sake of clearer comprehension, however, in the use that should be made of it, they shall be reproduced in the following order:

Correspondence of the parts, when inverting by contrary movement – First Form

Second Form

Here are other scales, not adduced, when treating imitation by contrary movement in two parts; and which scales may be employed when the chromatic style is adopted for modulating.

Chromatic by sharps – Third Form

Chromatic by flats – Fourth Form

Another example of this latter scale

Scale (Third Form) may be used when from the key of C we wish to modulate into its dominant; and Scale (Fourth Form) may be employed when from the key of C we wish to modulate into the sub-dominant. See the following example:

Before giving an extensive example of this kind of imitation, it will be necessary to pre-state that it is indispensable the inverse contrary response should commence before the period of each theme terminates, or else just upon the close of it; the theme, in its turn, should re-commence either before the response, or upon the close of the response. According to this rule, it will be perceived that the harmony and the parts must be combined in such a way that they shall adapt themselves to this disposal of the several commencements. The example will convey fuller comprehension of that has here been said.

Example of a regular piece, composed in inverse contrary imitation