3 and 4; Ex.

23, No.

2, fourth measure.
The distinction between the two species of cadence becomes most subtle when the _tonic harmony_ is chosen for the semicadence, _but with some other part of the chord than the keynote as uppermost (or lowermost) tone_.

This might appear to lighten the perfect cadence too immaterially to exercise so radical an influence upon the value (weight) of the interruption.

The _keynote_, however, is so decisive and final in its harmonic and melodic effect--everywhere in music--that its absence more or less completely cancels the terminating quality of the cadence-chord; in other words, the force of a tonic cadence depends upon the weight and prominence of the _keynote_.
For example: [Illustration: Example 36.