Often, a debate is not only about which conclusions about a topic are correct. It is as much, or more, about defining the topic itself.
Yet we are rarely able to pin down definitions precisely—sometimes not even vaguely . We can learn something from postmodernism here. While I don’t personally consider postmodernism a philosophically healthy place to stay, it’s an important place to pass through. The critical heart of postmodernist theory, in my view, is that the observer is an unavoidable part of their view of reality. Thus, the idea of an objective, rationalistic reality is untenable. (I like this article’s discussion of postmodernism.)
This idea leads to observation that human categorizations of the world are socially constructed. Social construction includes everything from contentious-to-define categories such as those around race and gender or seemingly-mundane categorizations such as eggplants. Social constructionism can quickly lead down the path to believing that subjectivity is all that there is. And if everything, even the definition of an eggplant, is subjective, who is to say that there is any such thing as an eggplant?
This is where the idea of nebulosity comes in handy. It provides a way for us to balance the idea that the complexity of reality destroys our ability to have a purely objective rationalistic account of reality with the observation that there is a something out there which provides the ground truth for our observations.
Nebulosity means cloud-like, without a fixed boundary.
When does a cloud stop being a cloud? We can provide various definitions based on observable properties of the cloud, but whether or not that definition is correct depends on the context in which the definition is used. If we are defining a cloud for the purpose of weather prediction we may use different criteria than if we care about finding shapes in the clouds on a lazy summer day.
One important thing to realize about nebulosity is that it is not just uncertainty. Uncertainty is a statement about one’s knowledge of the world. Nebulosity points to the idea that the fuzzy boundaries are part of the world itself, not just our perception of the world.
Why is this idea useful, especially with respect to definitional debates? Nebulosity helps us understand that while definitions are constructed and malleable, they are not arbitrary. The subjectivity comes in deciding where within the fuzzy, nebulous boundaries we draw the categorical line.
The idea of nebulosity also help us understand why some definitions are harder to pin down than others. To go back to the examples above, gender and race may consist nearly completely of fuzzy boundary. Eggplants have nebulosity (e.g., do you care culinarily or botanically?), but there is greater consensus on what is in vs out.
The practical upshot of this is that we should always think about definitions within a context and with a specific purpose. Definitions are not (generally) arbitrary, but they are dependent on how they will be used.
(By the way, eggplants were not chosen at random. The ideas in this post owe a lot to David Chapman’s in-progress works In the Cells of the Eggplant and Meaningness (which is where the nebulosity link above came from). Despite their incomplete state, I recommend both for encouraging some interesting thought explorations.)