Sentence:  In the case of discords, the fixed progression of the dissonant interval serves, to a large extent, as a guide to the progression of the remaining intervals of the harmony; in the case of concords this guidance is lacking, and it must be remembered that, in every progression of two parts, by similar motion, to a perfect concord (Fifth or Octave), there are bound to be hidden, if not apparent, <WSD>consecutives</WSD>. 
Meaning of the word marked with <WSD> tags:  A sequence of notes or chords that results from repeated shifts in pitch of the same interval.