Correcting form and cadence labels in an eight-bar passage
An analysis exercise gives an eight-bar passage in 6/8 with a key signature of two sharps. The first four-bar phrase ends with the melody on scale degree 2 over a bass on the dominant; the second four-bar phrase repeats the rhythmic idea but ends with the melody on scale degree 1 over a bass on the tonic. The bass of the first phrase moves stepwise from tonic to dominant; the second phrase reverses the contour. The accompaniment is homophonic, with repeated quarter-eighth patterns. A student labels the whole passage 'binary form' and the first cadence 'authentic'. The teacher asks you to correct the labels and explain how the phrase structure affects the harmonic reading. You may not add notes outside the given description.
1. Identify the cadence types and the relationship between the two phrases. Why is 'binary form' a weak label here?
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The first cadence is a half cadence, not authentic: it ends on the dominant with the melody on scale degree 2, which creates an open, unresolved effect. The second cadence is a perfect authentic cadence because it ends on the tonic with the melody on scale degree 1. The two phrases form a parallel period: the second phrase repeats the rhythmic and melodic idea of the first but closes the tonal argument. 'Binary form' is a weak label because binary form normally describes a larger two-part structure, often with repeated sections and a deliberate contrast or move to a related key. An eight-bar antecedent-consequent pair can be the first part of a binary form, but the passage as described is better labelled a period. The phrase structure matters because the half cadence sets up an expectation that the consequent fulfils; calling the first cadence authentic would wrongly make the passage sound closed too early.
2. If the second phrase were sequenced up a whole step instead of returning to tonic, how would your labels change?
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The passage would become a modulating parallel period or a two-phrase tonal sequence. The consequent would no longer close in the original key: sequencing the material up a whole step would point toward the supertonic major, so the final cadence would be a perfect authentic cadence in that new key rather than in the opening key. The first half cadence could still function as an opening gesture, but its meaning would change because the expected resolution is displaced. 'Binary form' would still be an overclaim unless the passage were shown to be a complete two-part structure with repeats or a clear second section. The analytical point is that sequence changes the tonal destination, not just the pitch level, so cadence labels must follow the key actually confirmed.