Isak made a comment that contains good points and plenty of discussion fodder, so I decided to respond to it with a full post. (My apologies for so singling you out, Isak.) He said:
It seems to me that there are concepts that are difficult or maybe even impossible to define, yet we still use, and there is a great degree of interpersonal agreement.
There are a great many concepts that we possess implicit definitions for, but not explicit ones. We cannot describe the definition or say how it is that we come to any conclusion involving it; for all practical purposes, they’re “black boxes” whose workings we can’t perceive. Data goes in, conclusions come out, and the only way we can guess at what goes on inside is to study the relationships we find between the inputs and outputs.
A good example is the famous statement by Supreme Court Justice Potter Stewart that “I can’t define [hard-core pornography], but I know it when I see it.” There have been entire books written on why that is not an acceptable legal principle, and why the standards for ‘acceptability’ are what they are. Chief among them is the simple point that no one could anticipate what Stewart would and would not ‘know when he saw it’, and so there is no way that people could direct their actions in accordance with the law. Who could tell whether any given act of speech would be appropriate?
Before we can toe the line, we must be shown where it is drawn. If the standard is not defined, not even the genuinely compliant can know how to obey.
I’m sure there were a finite number of principles, embedded in the structure of Potter’s mind, that determined how he would categorize stimuli presented to him as ‘acceptable’ or ‘not-acceptable’. But Potter was not aware of those principles any more than he knew how to regulate his blood salinity or how his liver acted to break down toxins. Parts of Potter ‘know’ those things, and act in complicated ways to maintain health. But the parts of Potter that speak, that communicate, that monitor parts of his mind and send the observations to the parts that communicate, they did not know those things. And so no one else could know them either.
In principle, a sufficiently detailed examination of Potter would reveal those operational definitions, in the same way that a close examination of the structure of a computer would reveal the nature of the program it implements. The information is not truly private. In practice, though, we don’t possess the technology or understanding necessary to do that, and even if we did it would probably kill Potter in the process. His applied standards were, in practice, private and subjective. See the following link for a more formal discussion of the problem of ‘obsenity’ applied to free speech.
What is a bird? A common practice problem given to students of cognitive psychology is the task of explaining what a bird is. Are penguins birds? Chickens? Chickens that have lost certain portions of their anatomy? Is a corpse a bird?
Everyone ‘knows’ what a bird is, and in everyday life, everyone seems to agree. But when you get down to the actual details, the arguments begin. People ‘know’ different things. And they have a great deal of difficulty expressing what they believe they know. The act of categorizing something as ‘bird’ or ‘not-bird’ requires little effort — people learned ‘what birds are’ as young children, and if doing so was difficult, they generally do not remember the difficulty. But explaining how they do so, especially in a way that would let others do the same, is almost impossible.
The hardest part of designing a scientific experiment isn’t coming up with a hypothesis, or thinking of a way to test it. Those aspects, although difficult, pale in comparison to the true obstacle: finding a way to operationalize the test. Defining precisely what observations would constitute an invalidation of the hypothesis, and being able to justify that definition, is what scientists struggle with most, at least in my experience.
In short, Isak: we are only capable of using concepts that we possess definitions for; a ‘concept’ without a definition is meaningless. We as individuals possess innate and implicit definitions for ideas that we developed without the aid of conscious design. These definitions are often an obstacle to communication, as they are idiosyncratic and not shared. People can use the same words to refer to very different things, and if this is not recognized, it can reduce the attempt to convey information to a frustrating and fruitless hash.
In conversation and discourse, the only concepts that can be used are those with meanings that can be given explicitly, that can be described in terms all sides recognize and accept as representing known values. Without this shared foundation, nothing can be built, nothing expressed, nothing conveyed.