The phrase "all classes of things" is correct and usable in written English.
It can be used when referring to a comprehensive range of categories or types of items or concepts.
Example: "The study aims to explore all classes of things that influence consumer behavior."
Alternatives: "all categories of items" or "all types of things".
The Mishnah's overriding proposition is that all classes of things stand in a hierarchical relationship to one another, and, in that encompassing hierarchy, there is place for everything.
In the example, the class Hypoglycemia is defined as the equivalent of the intersection of all classes of things that are "A concentration which is lower relative to the normal" (decreased concentration), "deviate from the normal or average" (abnormal), with respect to (towards) glucose, and inhering in "blood" (using the term portion of blood from the FMA).
(A universal is a quality or property that each individual member of a class of things must possess if the same general word is to apply to all the things in that class. Redness, for example, is a universal possessed by all red objects).
Armstrong, for example, champions universals as the best account of the difference between what he calls "natural" and heterogeneous classes i.e., between a class of things each member of which objectively resembles all other members in a single respect, and a class of things each member of which has little or nothing in common with other members.
For example, the word 'cow' singles out a class of things by excluding them from things they are not, all things assembled together under the concept "cow" are distinct from each other and do not share a single nature that the word 'cow' names.
Domains whose features are independent of each other and vary continuously lack the entitivity, in most cases, to be recognized as a class of things worth classifying.
There is, lastly, a class of things which are neither present in a subject nor predicable of a subject, such as the individual man or the individual horse.
It is not a property of things nor an accidental quality, not a substance, and not a class of things.
The Manual of Reason (TSD 3d) refines the idea: it defines a 'definition' of a class of things as any characteristic which is co-extensive with that class.
Again, in answer to the problem of unity and plurality — e.g., how can a thing be individual and distinct and yet a member of a class of things of the same kind?
