A Dictionary of Music and Musicians/Countersubject
COUNTERSUBJECT. When the subject of a fugue has been proposed by one voice it is usual for the answer, which is taken up by another voice, to be accompanied by the former with a counterpoint sufficiently recognisable as a definite subject to take its part in the development of the fugue, and this is called the countersubject; as in the chorus 'And with his stripes,' in Handel's 'Messiah'—
It should be capable of being treated with the original subject in double counterpoint—that is, either above or below it, as in the chorus just named, where it first appears in an upper part, but further on in the tenor, with the original subject in the treble; thus—
But it is allowable to alter it slightly when thus treated, so long as its character is distinctly marked. The principal subject of the above was a favourite with the composers of the last century; instances of it with different counter-subjects will be found in Handel's 'Joseph,' in Mozart's Requiem, and in a quartet of Haydn's in F minor; also in Corelli's Solos, op. 1, No. 3.
When a second subject appears simultaneously with the first proposition of the principal subject it is common to speak of it as the countersubject, as in the following, by Handel (6 organ fugues no. 3)—
but many theorists think that this tends to confusion, and wish it to be called a second subject. Cherubini held that a fugue could not have more than one principal subject, and that therefore the terms first, second, or third countersubject should be used to designate any subjects which follow after the first; but the question does not seem to be of any very great importance.
For further treatment of this question see Fugue.[ C. H. H. P. ]