There are some concept that most people (if not sometimes all people) fail to accurately define - eventually because the concept does not match a natural category - however we all have a good enough intuition about what is encompassed by the concept for most practical uses.

Is there a term that refer to the existence of such concepts with inexistant clear definitions but for which our common intuition is enough for practical usage?

Here are a few examples coming to mind:

  • Happiness
  • Complexity (outside of computer science, a dolphin feels more complex than a worm)
  • Game
  • Beauty
  • Awareness
  • Big (like in "it is a big number")

You, dear philosophers, experienced in working out the epistemology of such 'complex' concepts might have a much better notion than me of a commonly accepted definition of the above examples. Whether a definition exist for the above concepts is not so much the point of my post. My question is "Is there a term to describe such concepts?"

  • 5
    Vague concepts. Jun 6, 2017 at 18:05
  • 'word' There is no such think as an extant clear definition not dependent upon intuition to back it up. I think you are talking about anything other than an artificial model. And even such a model does not make sense until you get the intuition of what it was intending to model.
    – user9166
    Jun 6, 2017 at 21:06
  • 1
    You seem to be hinting at some of late Wittgenstein's ideas of "meaning as use" and "language game", and the related "meaning holism". Jun 6, 2017 at 22:19
  • the usual term is "concept" ;). few if any concepts can be "accurately defined." Like "red".
    – user20153
    Jun 6, 2017 at 23:02
  • 1
    What about just using the word "intuitive?" It's a bit circular, but quite accurate.
    – Cort Ammon
    Dec 5, 2017 at 18:57

5 Answers 5


Similar to this is the family resemblance concept - this is directed primarily against Augustinian notions of language and essentialism.

"We find that what connects all the cases of comparing [i.e. the use we make of the word 'comparing' (p. 86)] is a vast number of overlapping similarities, and as soon as we see this, we feel no longer compelled to say that there must be some one feature common to them all. What ties the ship to the wharf is a rope, and the rope consists of fibres, but it does not get its strength from any fibre which runs through it from one end to the other, but from the fact that there is a vast number of fibres overlapping. "(Wittgenstein, The Brown Book p. 87)


Is there a term that refer to the existence of such concepts with inexistent clear definitions but for which our common intuition is enough for practical usage?

No special term is required since unless we are omniscient all our concepts fall into his category. This would be why philosophers spend so much time defining their terms. Their concepts may not be correct in relation to the world but it's more important for communication and analysis that they're well-defined.

We use countless ill-defined words on the basis that there is a conventional understanding of them but not an exact technical definition. Space and time, existence, electrons, God, matter, mind, energy and so on. Even 'tree' has no exact definition. For most people even 'me' does not have one.

It would be more useful to have a word for concepts that have clear and exact definitions, for outside tautological or analytical systems (mathematics etc. where a thing is always what we define it to be) these are rare.


The classic example is salad. What is a salad? A mixture of lettuce, plus dressing? What about tuna salad? Pasta salad? Maybe its a mixture of savory ingredients plus some acidic liquid dressing? This would make spaghetti and meatballs a salad, and what about fruit salad?

If you really chase your tail on defining what salads are you'll come to wonder if the word means anything at all. And yet we all seem to competent in employing it somehow. The way to explain this phenomenon is by appealing to the Use Theory of language, which states that the meaning of terms comes not from abstract definitions but from how the words are used. Words are no longer carriers of pre-assembled meaning packets, but they are tools we can use to execute 'locutionary acts' (see J.L. Austin). If you try to figure out what a word means by trying to consolidate all of its usages, you'll get nowhere. The word 'Knowledge' is impossible to define in general, but any given usage is easily grasped because in each case the word is being used to express something slightly different (See Wittgensteins 'Family Resemblance' theory). If you want to know what a word means in some utterance, don't ask for the definition, ask how it is being used. We all know what salad 'means', not because we know the definition, but because we know all of the ways it can be used to express states of affairs, or do other locutionary acts.

Edit: To answer the actual question, I don't think there is an actual term to describe words that are elusive in this way, because all words behave in this manner to some extent. Rather, there is just a theory, namely Use Theory, which explains why we run into difficulties when trying to define words that are very versatile.


Perhaps this is an irreverent answer but I believe the phrase "je ne sais quoi" encapsulates what you are asking.

je ne sais quoi [zhuh nuh se kwa]/ noun, French.

  1. an indefinable, elusive quality, especially a pleasing one

All concepts are general, the concept of a tree, for example, rather than a particular tree, but the common notion you must know, which has slipped your mind, may be abstract concepts. What is abstract is not concrete or sensible.

There quite possibly may be another, better, term. Closer to the sense you indicate.

Speculative, formal, and other terms might be wanted. Ideal perhaps.

Addendum explanatory:

If I am not mistaken Aristotle defines Happiness as excellent activity of the soul. Eudaimonia belongs to the realm of psuke, and its specific difference, i.e., of all things attributable to the soul or to life, which is the same for Aristotle, is arete or the most-sound power.

Socrates speaks of things that "don't show up in a mirror". Of course, one can define anything, and thereby bring it into view in a way that judgment can ask if it is there or not, but reason (from which the definition is derived) is, these days, rejected as a faculty that can not properly demonstrate. It is, in this sense, dismissed from the realm of the proper sciences.

What is abstract is non-sensible. One can be referred to the Parmenides where three determinations are made concerning what are often called "properties", concerning the question about what concepts require ideas or forms of there own, and which do not. With the famous line about mud, hair and stones, sensible things, being of the lowest grouping. And then general material things in the second group, like fire and water.

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