what are consecutive fifths and consecutive octaves?

Answer 1

Consecutive fifths are 5ths that come one after the other with no other intervals in between. Same for octaves. The interval of a fifth means the notes are five notes apart, for example from C up to G would be the interval of a fifth. An octave - eight notes apart (actually the same note name but one will be higher) - for example C up to the next C.

In 18th and 19th century music theory the sound and use of parallel (consecutive) fifths and parallel octaves was considered bad practice. This primarily had to do with the movement of the outside voices - soprano and bass.

The sound of the 5th between outside voices was a very hollow sound and considered a "bad" sound and poor voice writing if they appeared in consecutive chords.

Consecutive octaves were considered bad because they are the same note so the soprano voice and the bass voice were playing the same melody line. This reduced independence of the musical parts.

Parallel fifths and octaves are now often used in the style of many 20th and 21st century composers.

Hope this is a help. Musician,composer,director.