The attempt to categorize “things” goes back a long time in the history of human ideas, but I have found the work of three people to be the most helpful in structuring my own version of this knowledge.
The first is the great German philosopher Arthur Schopenhauer (1788-1860). According to various biographical data, in adulthood, he was a fairly curmudgeonly individual. Just my type! His PhD dissertation in 1813 covered the different types of things. Schopenhauer distinguished concrete objects from constructs, and separated out geometric forms from both. I’m not going to talk about geometric forms any further in this series.
The second is David Levy (who is still living and teaching psychology at Pepperdine University). His masterpiece, Tools of Critical Thinking: Meta-thoughts for Psychology, does not separate out geometric forms but does call out events as part of the category of concrete objects. His primary criterion for calling something concrete is that it can be measured. A religious ceremony, such as a wedding or funeral at a church, or a sporting event takes a certain amount of measurable time and happens in a specific location (or locations) with defined longitude and latitude. Yet, to me, this type of event – including, for example, a concert, a dramatic performance or movie showing – has meaning that goes far beyond these basic physical features. The significance of any of these events is only loosely related to the measurable attributes. For this reason, I like to put “events” in their own category.
The third person is the great Indian sage Kanada. The range of years estimated for the life of Kanada (6th-2nd century BCE) overlaps with the classical age of Greece (5th and 4th centuries BCE). Some scholars have noted that Kanada never mentioned Buddhism, so he is likely from the earlier part of the estimated range. That would have him ahead of the great Greek philosophers, whose names are known by all educated people worldwide.
For me, Kanada has the clearest description, or definition, of qualities. Colors are qualities. We can have a red apple or red paint or red ink or red blood. But the reason that these things may appear red may differ. Red is not “a concrete thing.” Red is something that humans can experience, but it’s always an aspect of something else.
Concrete red objects are not red unless and until they appear red to someone. That’s a key point. An observer is required to judge that the thing is red. Another way to say this is that seeing red is a subjective experience.
This is true of all “qualities.” Other qualities that Kanada specified in his philosophical system include color, taste, smell, touch, pleasure and pain. These are all essentially sensations.
The most interesting thing about Kanada’s philosophy is that way back when he was teaching and philosophizing, he created a system of knowledge that integrated the consciousness of the observer into the object being observed.
Noticing qualities is an aspect of this. Kanada had important insights about the material world and the sensory systems with which humans experience it. This appears to have happened well before any other human.