“Everything is vague to a degree you do not realize till you have tried to make it precise.” – Bertrand Russell
One of the purposes of philosophy is to define and clarify concepts by finding their necessary and sufficient conditions. A classic example used to illustrate this is the concept of a bachelor.
“What is a bachelor?”
“Well, an unmarried male.“
“What about a baby boy, he’s an unmarried male, but certainly not a bachelor.”
“Ok, an unmarried male of marriageable age.”
“What about the Pope? He’s an unmarried male of marriageable age, but not a bachelor.”
“Hmm, alright, an unmarried male of marriageable age and marriageable status.”
So by the process of proposing definitions and counter-examples we eventually get a set of necessary and sufficient conditions. Except, not quite.
“Define marriageable status.”
“It means you are able and willing to get married.”
“Ok, but if all bachelors must be able to marry then none of them must be willing to marry, otherwise they’d all get married!”
“Hmm… Alright, they just need to be willing to get married at some point in the future.”
“Well what about the so-called confirmed bachelor, they do not wish to marry at all, but they are still bachelors.”
It doesn’t stop there either. What about unmarried men in a committed relationship, how long does the relationship need to last before they stop being bachelors, what about open-relationships, how do you even define “committed relationship”? And so a concept as simple as bachelor becomes mired in complexity upon examination. Now think of all those concepts that are obviously complex even on the surface –justice, good and evil, consciousness, knowledge, etc.– and imagine how much more complex they become.