8- or 16-bar themes

Apologies if this is a really basic question, but it is very non-obvious to me because I'm a mostly-self-taught amateur composer... I've been noticing on various composition resources out there that people keep referring to 8-bar or 16-bar "complete" melodies or themes. Why 8 bars or 16 bars specifically, as opposed to, say, 6 bars or 13 bars?

The thing is, in most of my compositions I rarely have 8- or 16-bar themes. I find myself having 5-bar melodies, which lead to 9-bar / 10-bar themes, or 6-bar themes, or 3-bar motifs that lead to 6-bar/9-bar themes, etc.. Is this normal??

Also, I find that my compositions often have "run-on sentences", so to speak, where a 5-bar motif has its final notes in common with the opening notes of the subsequent motif, so the result is 1 bar "shorter" than it "should" be, if they have had no notes in common. Is this normal, or is it a sign of some kind of deep structural defect in my music?

Do these "odd-length" melodies/themes have any longer term structural implications, besides their "unusual" length? Are they an actual issue I should be aware of, or am I over-thinking music theory here?

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  • I was just reading a physics book in which the author argued that the universe is extremely complicated; and that we cannot affirm with absolute certainty that  it functions on a mathematical square.  This would appear to be the case on both the macrocosmic and microcosmic scale.


    I think I also read somewhere that the number of possible melodies is greater than the total number of stars in the entire known physical cosmos.  So music may be potentially more complicated than the universe itself.


    At the quantum level, the motions of physical energies and smaller particles are virtually unpredictable, and the most complex equations are needed simply to describe the probable vacillations of one electron in relation to one proton in hydrogen atom. 


    In universal or world music there are an infinite number of possible sonic intervals involving the aural space between A natural and A sharp.  That does not even include all possible timbres, which up the quantity to a higher order of infinity. 


    There is no single set of rules for composition that could possibly describe even the smallest set of diverse musical creations that exist across and within the wide totality of universes which constitute what we now (in accordance with modern cosmology) quite aptly call the Multiverse.








  • Not on both scales. The quantum world does indeed appear to function in an unpredictable way. But the world it has given rise to - the world of stars, planets, tables and chairs - does function predictably. And there is scarcely a piece of it where the mathematical square does not put in an appearance!

    However, I take your point about composition in general. The possibilities are virtually - if not actually - endless.

    The mark, I would suggest, of a real composer is courage: The courage to choose one option from countless, and to commit to this choice endlessly!
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