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I'm working through Mark Sarnecki's Rudiments of music theory book, and I'm digesting the bit about augmented and diminished intervals.

I'm confused as to how a diminished unison can exist. By definition it would be one semi-tone smaller than a perfect unison, which cannot exist.

Am I missing some key idea somewhere? Thanks so much!

Edit: I don't believe the question is a duplicate, although it appears that way based only on the question headings. I posit that when the question bodies are taken into account, the questions are distinct.

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  • Even if the referred question seems to be somewhat different; what does the accepted answer not cover from your question? – guidot Nov 10 '17 at 8:56
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    Thanks for following up and giving me a chance to explain. An expert can likely find the answer to this question within that answer. But to a newbie like me, it seems to be talking about chords, not intervals. – Kyle Schlitt Nov 15 '17 at 3:58
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    The "duplicate" question refers to a diminished first (i.e. root) in a chord, rather than a diminished unison. There is nothing in the accepted answer that specifically spells out that there is no such thing as a diminished unison, although it does say that a half step written as a unison is always an augmented unison. I vote to reopen the question, as someone looking for the answer "no, there is no such thing as a diminished unison" would have a very tough time finding it in the other post. – BobRodes Nov 17 '17 at 4:53
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The unison is an exception to this due to how the unison works.

A perfect unison has a distance of 0 semitones from the original note while and augmented would have a distance of 1 semitones. Since the interval is perfect at a distance of zero one less would be -1 semitones, but since most theorists only consider intervals as a positive number a diminished interval would be impossible.

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