Every part of the book, the article, has a beginning. Each chapter, each subheading of a chapter, each paragraph. Even the conclusion has an introductory paragraph with an opening sentence. Every sentence has a first word.
Every musical note has an attack, or onset. Curiously, a large part of the identifying timbre of the note is determined by its attack, so that if you took away the onset by electronic editing, you would not longer be able to tell what instrument is playing. The articulation of a musical phrase consists of the way the attacks of individual notes are linked Staccato or legato? (or not linked). Is the trumpet-player double tonguing? Does the violinist lift her bow, or switch its direction, in the middle of the phrase? I notice how the violinists in the orchestra typically use the entire length of the bow, from top to bottom or bottom to top, keeping the bow on the strings with very little interruption.
So writing is a process of constantly beginning, then continuing something for a while, then beginning again. Fluency is continuity, flow, while articulateness is differentiation (hearing each note distinctly) within an ongoing flow. Short sentences in succession might feel articulate but choppy.
The other part of the musical notion is the sustain or decay. That might require another post.