At other times they are of very considerable extent —
In long subjects such as these, we very often find sequential passages introduced. As a general rule, the slower the time, the fewer should be the bars in a fugue subject. It is important that the hearer should readily recognize the subject when it reappears, and this is much more easily done if it be concise than if it be long and straggling. Many of the finest fugues existing are those written on short subjects. It should be added that the length of the subject in vocal fugues will partly depend on the words, as the cadence should always come where the sense of the text allows it. Think, for example, how absurd it would be if the fugue subject at § 28 (a) ended with the words, "and he shall reign for ever and"—!
47. Another important matter to be considered is the compass of the subject. In vocal fugues this should rarely exceed an octave, because if it does, it will be very likely when it appears in other keys to go beyond the comfortable range of the voices. Exceptions are occasionally to be met with, as, for instance, in one example (a) of § 40, which has the compass of a tenth; but these are rare. In instrumental fugues a larger compass is possible; but even then it is seldom expedient, because of the probability of its causing much crossing of the parts, and so impairing the clearness of the fugue. Many of the best fugue subjects lie within a small compass. In two of the finest fugues of Bach's "Forty-Eight" (Nos. 4 and 33) the compass of the subject does not exceed a fourth. In the examples given above at § 32 (b) and § 34 (b) the compass is only a fifth; while at § 28 (c), § 30 (b), and § 34 (c) it is only a sixth.
