the major sixth chord (C6) C-E-G-A • the minor sixth chord (Cm6) C-E b-G-A • the “sus4” chord (C7sus4 or just C7sus, “sus” meaning “suspended”) C-F-G-B b. The first two are usually seen as enriched perfect chords, in which case the sixth is considered an enrichment, like the ninth, eleventh, or thirteenth. The third case is less straightforward and depends on the context. In a tonal situation, the “sus4” chord is a form of suspension.10 In other contexts, it will be considered a specific chord. The question is asked of the distinction between the fourth and eleventh on the one hand, and the sixth and thirteenth on the other hand. How do we decide that F in a C chord is a fourth or eleventh or A a sixth or thirteenth? The reality shows that it is a total mess in the practice of jazz musicians. When a figuring including “4” or “11” (even more so with “6” or “13”) occurs, it is impossible to know for sure what exact degree the author is referring to. It seems to me that the rule should be this: if there is a fourth then there is no third, and if there is a sixth then there is no seventh. Implicitly, this comes down to considering that the fourth is a substitute for the third (as mentioned before, this is easy to understand in a tonal system) and the sixth a substitute for the seventh. This is a consequence of chords being built up on superimposed layers of thirds (which confirms the structuring nature of such a build-up, by the way). For F to be an eleventh, the third (E or E b) must have existed beforehand. The same applies for A to be a thirteenth: a seventh, B or B b, must have existed beforehand. Yet, the “7/6” figuring often occurs, which contradicts this rule (the “13” figuring should include the seventh implicitly). This does not reveal a different approach to that chord but a lack of rigor in figuring practices, with the implicit idea behind it that, as jazz is a type of music based on oral traditions and practices, any localized ambiguity can be clarified at a later stage.