Natural Kinds and Definitions


If the thing under consideration has an essential nature, a “sine qua non” then an adequate definition for the concept would identify all the necessary and sufficient qualities of the thing defined such that the definition picks out all and only members of the set named by the concept.  But more than that, the definition would not simply assemble a set coextensive with the set of items of the class under consideration, it would tell us what makes each item a member of the set.  This is, famously, what Socrates is always looking for in the early Platonic dialogues.[1]  (What is it that all and only things of that kind have in common, and in virtue of possessing are things of that kind?)


The concepts of necessary and sufficient conditions help us understand and explain the different kinds of connections between concepts, and how different states of affairs are related to each other.


Sufficient Conditions


To say that X is a sufficient condition for Y is to say that the presence of X guarantees the presence of Y. In other words, it is impossible to have X without also having Y. If X is present, then Y must also be present. Again, some examples:


·         Being a square is sufficient for having four sides.

·         Being divisible by 2 is sufficient for being an even number.

·         Being a person born in the US is sufficient for being an US citizen.


To show that X is not sufficient for Y, we come up with cases where X is present but Y is not. Examples :


·         Loving someone is not sufficient for being loved. A person who loves someone might not be loved by anyone. L

·         Loyalty is not sufficient for honesty because one might have to lie in order to protect the person to whom one is loyal.

·         Being a US citizen is not sufficient for being a US voter (e.g. One might be a citizen, but under age, unregistered or a convicted felon.)


Additional remarks about sufficient conditions:


Expressions such as "If X then Y", or "X is enough for Y", can also be understood as saying that X is a sufficient condition for Y.  “If X then Y.” is stating that the truth of X is sufficient to guarantee the truth of Y.  The same state of affairs may have more than one sufficient condition. Being blue is sufficient for being colored, but of course being green, being red are also sufficient for being colored.  So not, being blue is NOT a necessary condition for being colored.


So in the conditional “If you pass the final, then you will pass the course.” it states that passing the final is a sufficient condition for passing the course.  (But note: it may not be necessary.)


Necessary Conditions


To say that X is a necessary condition for Y is to say that it is impossible to have Y without X. In other words, the absence of X guarantees the absence of Y or the falsity of X assures us of the falsity of Y.  A necessary condition is sometimes also called "an essential condition".


Some examples:


·         Having four sides is necessary for being a square.

·         Being brave is a necessary condition for being a good soldier.

·         Not being divisible by two is necessary for being a prime number.


To show that X is NOT a necessary condition for Y, we simply find a situation where Y is present, but X is not.  Being born in the US is NOT a necessary condition for being a US voter.  My neighbor is a voter, but she was not born in the US.  She is a naturalized US citizen.




·         Being rich is not necessary for being happy, since a poor person can be happy too.

·         Being Chinese is not necessary for being a Hong Kong permanent resident, since a non-Chinese can become a permanent resident if he or she has lived in Hong Kong for seven years.


Additional remarks about necessary conditions:


We invoke the notion of a necessary condition very often in our daily life, even though we might be using different terms. For example, when we say things like "life requires oxygen."  This is equivalent to saying that the presence of oxygen is a necessary condition for the existence of life.


A certain state of affairs might have more than one necessary condition. For example, to be a good concert pianist, having good finger technique is a necessary condition. One cannot be a good pianist if one does not have good finger technique.  But note, good finger technique is NOT sufficient (not enough).  Another necessary condition is being good at artistically interpreting piano pieces.


So in the conditional “If you pass the final, then you will pass the course.” not passing the course implies you did not pass the final.  In other words, according to this conditional, not passing the final is a necessary condition of not passing the course.  There is no way one could fail the course without also failing the final.  But it may not be sufficient.  In other words, even if the conditional is true, it is possible that you pass the course without passing the final.  The conditional only tells us what will happen if you PASS the final.  It tells us nothing about what will happen if you do  NOT pass the final.


Think “SUN”


So when it comes to conditional statements (i.e. If P then Q) the antecedent (P) states a sufficient condition for the truth of the consequent (Q) though NOT a necessary one, and the truth of the consequent (Q) is a necessary condition for the truth of the antecedent (P) though not a sufficient one. 


If P then Q = If S the N


1.       P is sufficient for Q

2.       Q is necessary for P

Note further then, that the denial of the consequent (~Q) states a necessary condition for the denial of the antecedent (~P).


If ~Q then ~P = If S the N


1.       ~Q is sufficient for ~P

2.       ~P is necessary for ~Q


Four Possibilities


Given two conditions X and Y, there are four ways in which they might be related to each other:


·         X is necessary, but not sufficient for Y.

·         X is sufficient, but not necessary for Y.

·         X is both necessary and sufficient for Y. (or "jointly necessary and sufficient")

·         X is neither necessary nor sufficient for Y.


This classification is very useful when we want to clarify how two concepts are related to each other. Here are some examples:


·         Having four sides is necessary, but not sufficient for being a square (since a rectangle has four sides but it is not a square).

·         Having a son is sufficient, but not necessary for being a parent. (A parent might have a daughter only).

·         Being an unmarried man is both necessary and jointly sufficient for being a bachelor.

·         Being a tall person is neither necessary nor sufficient for being a successful person.


Pitfalls of Definitions


The (Hard) Case of “Religion


Imagine we were trying to define “religion.”  That is, imagine we were trying to name the necessary and sufficient conditions of what it is to be a religion, what it is that all and only religions have in common and, in virtue of possessing that, are religions.


Too Narrow


In some cases the definitions are too narrow.  One example would be defining religion in terms of the speaker's own religious beliefs or those of his or her culture and tending to exclude the religious beliefs of other cultures.


Too Broad


Others have been so broad as to include practices and ideologies which we would not want to call religions.  Indeed would seem to be the opposite of what a religion is. 




Still others fail because they presume a religious understanding of terms and so, in some sense, end up defining religion in terms of itself.


“The Paradox of Analysis”


Since the days of Plato, philosophers have worried about the “paradox of analysis.” Plato put it this way.  The pursuit of truth is either unnecessary or impossible.  Either we know the truth already and thus the pursuit of truth is unnecessary, or we don’t know the truth and thus we would not recognize it even if we found It.  His solution to this problem was that we know the truth but we forgot it. Philosophical discourse serves to remind us of the truths that are in us innately.


The Paradox of Analysis is pretty much the same problem.  Either we know what the word “religion” means, and thus there’s no need to define it further.  Or we do not know what the word means and therefore would never know an adequate definition even if we found one.


A defender of the search for definitions might suggest that, while we might have a pre-theoretical understanding of “religion,” this can be sharpened and clarified through discourse and debate.


In Search of a Definition: The (Hard) Case of “Religion”


How should we define “religion?”  What is it that all and only religions have in common by virtue of which they are religions?  We would want then to make a definition of religion that is not overly vague and general, but that still is “inclusive enough” so as not to leave out practices it would be practically beneficial to include.  Ah, but this raises a further question: Beneficial for what purposes?  It seems that a definition that might be useful to the economist might not be useful to the art historian, etc.


·         Is there an “essence” to religion?

·         Does it form a natural kind?

·         Is there something that all and only religions have in common in virtue of the possession of which they are religions?


So is religion a natural kind with an essence to be discovered and named?   The ubiquity of religion may suggest an innate “religious instinct.”  Rudolf Otto certainly seems to think that religions do form a sui generis. (He actually quite adamant about that.)


Nominalism vs Realism


Nevertheless, there are other objections to even the search for the definition (e.g. of religion) or the search for  “essences.”  Some would argue that the search for a definition (e.g. religion) is fundamentally misconceived.  It is premised on an unsupported assumption. It presumes that religion is a “natural kind” and therefore has an essence which can be defined. However, if religion is NOT a natural kind there may be no “essence” to discover, no set of necessary and sufficient conditions, no definition to be discovered.


Those who hold a “nominalist” view of universals would suggest that a common noun (say, “sandwich”) names a set of objects culled together by our linguistic practices.[2] Think of it this way: there is a box someplace with the label “sandwich” on it.  Whatever is in the box is a sandwich. To say that something is a sandwich is merely to say it is in the box. On a similar nominalist conception of religion, to say that something is a religion is only to say it is in the “religion box.”  It is not to name a set of properties or some fixed nature.  It is only to identify it as a member of set we create through our social/linguistic practices.


“But how do things get into the box?” one might ask.  Things get into the box simply because the social/linguistic practices of our community put them there. The only principle which guides this sorting of objects are practical concerns. For instance, today there seems to be some debate as to what a marriage is. Some ask whether or not three-partner arrangements/ marriages are really marriages or not.  They are presuming that there is an essence to marriage or that marriages are a “natural kind and we must discover whether having exclusively two members is an essential feature of marriages or not.  Are these arrangements really members of the species or not.  Alternatively, the very question presumes that there are necessary and sufficient conditions for being a marriage, and the task at hand is to decide whether or not these meet the requisite conditions or not. 


A nominalist about this matter would caution us not to think there is a truth to be discovered. Rather we should ask ourselves what the practical benefits would be from expanding our “definition” of “marriage,” putting things in the box that were not in the box previously.  Notice the very different cognitive task then.   This is not the “logic of discovery,” but rather the logic of creative practicality.   If we take that approach to our investigation of something (e.g. religion), then we should see this not as an exercise in discovering an essence (of religion), but rather, investigating what practical advantages arise from using or discarding this or that definition, sorting one way rather than another. 


Alternatively, an anti-essentialist about religion may ask:


·         Is there no “there” there? (Why should we imagine there is a common essence to “religion?”)

·         Is “religion” merely a conjurey of social/linguistic practice? Like the consolation “The Big Dipper” it does indeed refer to something that is, at least for the time being, fixed and objective, but it is, nevertheless, “created” by social/linguistic practice.

·         Is this a linguistic sorting of phenomena such that we are constantly defining and redefining what a religion “is” and the only thing guiding this sorting process is practical value?


Often they argue that the very diversity of conflicting religions is evidence that religion is more a socially manufactured and acquired characteristic of human life, perhaps one we might do well to abandon.  (Daniel Dennett seems to suggest as much.)


·         Hard to say what they have in common.


For instance, you may be inclined to cite "belief in God or gods" as a criterion for calling something a religion.  But this suffers from two problems immediately:


1.       one of the largest religious traditions in the world-Buddhism-has no such concept.

2.       It is not immediately clear what one means by “god” or “God”  (People have meant importantly different things) so asserting that any religion must affirm its existence is not really that helpful on its own.)


We may try to identify religions by using social or historical criteria:


·         Institutional organization

·         A church

·         Prayer gatherings

·         A priestly class


But there are Christian Protestant sects who believe that religion is ultimately a private affair for which no congregation is necessary.




Many believe that the word ‘religion’ derives from the Latin verb ‘ligare,’ ‘to tie’, with ‘re”- thus meaning ‘to tie back’




·         Latin root

·         Re plus ligare

·         ‘again’ combined with ‘to bind’ meaning ‘to tie fast’


Others suggest that the word derives from a different Latin word: Religia


·         Religia

·         Latin – ‘obligation’ or ‘bond’

·         Religian


The words ‘religion’ and ‘religious’ can indicate:


·         the recognition of an unseen higher power

·         the reverence for a higher power

·         a commitment to a system of faith or worship


Religion is a ‘world view’, a set of beliefs which shape the way a society sees the world.  But it seems set apart from merely an ideology in that the worldview frequently entails uniquely religious concepts:



·         This concept refers to an existence beyond the world.

·         This idea is present in Judaism, Christianity and Islam.



·         The belief that the divine is present or manifest in the phenomena of the natural world

·         Linked to Hinduism and Buddhism


Sacred and Profane

·         Sacred: That which is wholly “other,” set apart for worship (a deity or other object worthy of worship).

·         Profane: Nonreligious.  Outside the sphere of religion.


Mircea Eliade


“The sacred always manifests itself as a reality of a wholly different order from ‘natural’ realities. ...The first possible definition of the sacred is that it is the opposite of the profane.”


Seven Dimensions of Religion


So then, perhaps rather than a strict definition of religion, it would be more helpful to identify common features that help us understand the way academics think about religion.


Scholar of World Religions, Ninian Smart, identifies seven dimensions of religion.


1.       practical ritual dimension – worship, prayers (Formal/ Informal, Temporal and Spatial)

2.       experiential/ emotional dimension (Numinous/ Mystical Experience)

3.       narrative and mythical dimension – stories, texts a vehicle that relates a truth defying normal expression and sets pattern for human behaviors/ Cosmogony Accounts of creation of the world, or Eschatological accounts/Beliefs about the end of the world Scriptural or canonical (Greek kanon measuring riod)

4.       doctrinal and philosophical dimension – beliefs (Typically explaining complex ideas. May or may not be familiar to the average believer, but is part of the scholarly tradition.)

5.       Ethical and legal dimension – laws, ethics, action guiding directives that can extend to diet and dress.

6.       Social and institutional dimension – the group, society

7.       Material dimension – art, architecture,





         Natural World


Three Types of Religion


Another way of categorizing religion is as Exoteric, Esoteric and Both


1.       An exoteric religion generally emphasizes dogma and ritual.  There are certain codes, creeds, practices and symbols that followers must adopt in order to be recognized as true followers.  Rigid adherence to these is required for membership.


2.       An esoteric religion focuses on the inner life of the souls placing less emphasis on outer practices.  Followers determine their own lifestyles.  But however they choose to live their lives, they must remain mindful of their inner spiritual life.  This sometimes results in followers who consciously or unconsciously follow more than one tradition or religions.


3.       A balance of both esoteric and exoteric religion, is one that encompasses both virtues.  Outer practices are signs of devotion, that shape the follower’s inner core.  Are you comfortable with your "truth"?  How certain are you of this Truth?


Twentieth century philosopher John Wisdom, a student of Ludwiq Wittgenstein, claims that the essential feature of religious belief is a certain "attitude" that the religious person has toward his or her surroundings and that the gap between the religious "attitude" and that of the philosopher or scientist who is interested in explanation is unbridgeable.


General Concluding Remarks on Definitions ​


The 20th Century philosopher, Ludwig Wittgenstein (1889 – 1951), suggested that there are many terms for which we cannot provide necessary and sufficient conditions and yet, we perfectly well know what the terms mean.  “Game” was such a term for Wittgenstein.  According to him, among the many things that count as games there only exists a “family resemblance,” but no neat set of necessary and sufficient conditions.  He argues that the Platonic search for a common form for all the member of a kind was simply a 2500 year old wild goose chase, of sorts, having nothing to do with truly understanding a what a term means.  For Wittgenstein, knowing what a term means is really just knowing how to correctly use it in the language in which it arises.  Just knowing what a rook “is” means correctly using it in a game of chess, knowing what a game is means correctly deploying the term in the “language game” in which is occurs.  


​Morris Weitz, in his article "The Role of Theory in Esthetics,“ suggest much the same about the word “art.”  While “Byzantine Painting” or “Ancient Greek Tragedy” might be concepts we can define with strict conditions, this is because they denote “closed concepts.”  That is these traditions have ended cease to develop.  By contrast, “Art” is an “Open Concept” and thus defies definition.​  Given its dynamic “living” nature, the items counting as art may increase in diversity in unpredictable and unforeseen ways.

[1] For instance in the dialogue Euthyphro Socrates asks Euthyphro to give him a general definition that identifies that feature or features that all holy deeds share in common.

[2] This is similar in a way to Ludwig Wittgenstein famous critique of definitions contain in Philosophical Investigations.

Consider for example the proceedings that we call "games". I mean board-games, card-games, ball-games, Olympic games, and so on. What is common to them all? Don't say: "There must be something common, or they would not be called 'games' - but look and see whether there is anything common to all. - For if you look at them you will not see something that is common to all, but similarities, relationships, and a whole series of them at that. (Sec. 66)

Curiously, William James in The Varieties of Religious Experience had made the very point about "religion" that Wittgenstein later made about "game" and Wittgenstein had read James' work.  However, it is not clear when Wittgenstein read James.