Aristotle by pengxuebo


Posterior Analytics – Lecture III
         Today’s Class

• Post. An. Book II
 • Definitions
 • Essences
 • Grasp of First Principles
               Book II
• Opens with an account of definition
 • Aristotle’s science is an attempt to
    discover the real natures of kinds
  • An Aristotelian definition gives us an
    account of each of these kinds
  • Aristotelian definitions are objective, not
    stipulative or conventional
                 Four Questions
 • When we ask about anything, there are four
       kinds of question we can ask, corresponding
       to four things we can know
     1. The “that” (ὅτι) e.g. “Is it so that A is B”
     2. The “why” (διότι) e.g. “Why is A B”
     3. If it is (εἰ ἔστι) e.g. “Does A exist”
     4. What it is (τί ἔστι) e.g. “What is A”*
* This is the “essence” of a thing. Essentia is the Latin term for Aristotle’s “What it is to be”.
   Aristotle’s Examples
1. Does the Sun suffer eclipse? (fact)
2. Why does the Sun suffer eclipse? (reason)
3. Do Centaurs or Gods exist? (existence)
4. What is a God? What is a man? (essence)
• To know why something happens, you must
  already know that it is the case.
 • e.g. So to know why the Sun is eclipsed,
    you must first know that it is in fact
   • Therefore: questions of type 2 depend
      on answers to questions of type 1
• Aristotle thinks that questions of type 4 are
  dependent on answers to questions of type
  • e.g. we cannot know what a Centaur is
    (i.e. know the essence of Centaurs) unless
    Centaurs exist
    • But this is controversial
What about Non-beings?
• It seems that we can know what a unicorn
  is, or a dragon, or even a dinosaur, without
  these things existing (some of them have
  never existed).
• Moreover, compare Socrates in some of
  Plato’s dialogues, who thinks that we must
  know what X is before we can know that X
• In other words: how can you answer the
  question of whether zebras exist, if you don’t
  know what zebras are?

 • If I didn’t know what zebras were, I would
    walk around forever trying to find them. I
    would even walk right past them, because I
    don’t know what it is to be a zebra.

 • So how could I ever start?
    Aristotle’s Answer

• If I ask you to find a zebra, you may ask me
  what I mean by “zebra”.
• So I say “A stripey donkey”
• That is sufficient for you to find zebras if
  they exist
• But it is not the essence of being a zebra
• In other words, our ordinary descriptive
  definitions of things may not be the same as

• Our meanings are not the same as
  Aristotelian essences.

• Our meanings are conventional or stipulative,
  whereas Aristotelian essences exist
  independently of our thought or speech
• I may find a zebra due to the description you
  give me, and when I do find it, I can try to
  determine the essence of a thing.

• e.g.You could tell me to look for things “like
  this” when you point to a triangle, but that
  does not tell me the essence of a triangle.

• I can come to know the essence of triangles
  through the clearly known particular
  (induction to the universal).
• Aristotle is right. Questions about the
  essence of things clearly require the
  existence of those things, since essences are
• This also counts for formerly existent things
  like dinosaurs. There is such a thing as “what
  it is to be” a dinosaur, only if dinosaurs
  actually existed.
  Definition (ὁρισμὸς)
• An Aristotelian definition states the essence
  of a thing (sometimes called the “formula”).
• e.g. Man = rational animal
• To give the essence of a thing (i.e. a species),
  you need to give its genus and differentia.
  • Animal = the genus; Rational = the
• An Aristotelian definition looks like a
  dictionary definition

• But it expresses the nature of a real
  objective kind

• Dictionary definitions need not (e.g.
  unicorns, dragons, etc.)

• Dictionary definitions can be wrong, but
  Aristotelian definitions must hold of their
  subject to be definitions at all
    Cause and Essence
• Aristotle: the cause of something is the same
  as its essence
  • e.g. an eclipse
   • The essence of an eclipse is the
      obstruction of light by a heavenly body
      • Eclipses happen because heaven
        bodies obstruct light (cause)
• Why are whales warm blooded?
 • Because they are mammals
    (commensurate universal)

   • But the essence of being a mammal is to
     be a warm blooded animal

     • So the essence supplies the cause
     Another Example
• Question: “What is a concord?” (essence
• Answer: “A concord is a numerical ratio of
  high and low pitch” (essence)
• Question: “Why is the high note concordant
  with the low?” (causal question)
• Answer: “Because it has a numerical ratio”
    Aristotle’s Science
• Aristotle assumes that the fact that whales
  are warm blooded is a necessary feature of
  the world (it could not have been
• But we might think that this is just a
  contingent feature of reality
  • e.g. Necessity must be a priori (there are
    no a posteriori necessities)
         Against Aristotle
•   Modern Empiricist philosophers (from Locke
    and Hume onwards) insisted that the only
    necessities are those yielded by Analytic
•   Early 20th century Analytical Philosophers
    (such as the Logical Postivists) accepted this
    •   There are no empirical necessities, only
        logical (analytic) necessities
       Frege & Russell
• Both Frege and Russell were interested in
  the question of how names have meaning.
• Both rejected the view that the meaning of a
  name is its referent
• Frege divided meaning into Sense and
• Russell argued that names were disguised
•   Because if meaning is just reference, then “The Morning
    Star” and “The Evening Star” have the same meaning,
    because each refers to the same thing (the planet Venus).

•   But someone could believe that the Evening Star is
    different from the Morning Star

•   How could they believe this if the terms have the same

•   It would be like someone believing that the Morning Star
    is not the Morning Star, which is a contradiction.
The Frege/Russell Solution
•   We must distinguish between the referent and
    the way in which a word presents the
•   e.g. “The Morning Star” and “The Evening
    Star” present the referent under different
•   Frege claimed that although these terms have
    the same reference, they have a different
• So although Clark Kent is identical with
  Superman, Lois Lane can believe that Clark
  Kent is not Superman, since the sense of
  “Clark Kent” is different than the sense of

• Senses are different ways of “having things in

• What we would call “sameness of meaning”
  is really sameness of sense.
• Russell’s view is that names are disguised

• A Russellian description serves the same
  function as a sense (e.g. the star that appears
  in the morning)
•   On this view, necessity is a matter of analyticity

•   Analytic truth = truth by virtue of meaning

•   So “All triangles are three sided figures” is
    necessarily true because “triangle” and “three sided
    figure” have the same meaning.

•   Analytic truths are true by definition.

•   They are also all a priori statements (statements that
    are true no matter what is true in the world)
• “Water is H O” is not a necessary truth,
  because the terms have different senses.
  • Someone could believe that water is not
    H2O without believing that water is not
    water (there is no contradiction here).
• An Aristotelian would argue that “Water is
  H2O” is a necessary truth, because this is
  the essence of water (what water is).
• Similarly, an Aristotelian would argue that it
  is essential (i.e. necessary) to being a pig, that
  pigs cannot fly.

• But on the Frege/Russell view, “Pigs cannot
  fly” is not a necessary truth, because it is not

• On this view “pigs cannot fly” is a contingent
  statement, because someone who says they
  can is not involved in a contradiction
     Putnam & Kripke
• One consequence of the Frege/Russell view
  is that there are no empirical necessities
  (statements about the world are not
  necessary truths – all necessity is a priori)
• In the late 20th century, some philosophers
  argued that this cannot be right.
• Saul Kripke and Hilary Putnam authored the
  most famous arguments.
        Hilary Putnam
• Putnam argues that definitions cannot be “in
  the head”
• e.g. Take two planets “Earth” and “Twin
  Earth”, which look alike to all observers
• But even though it looks the same, what we
  call “water” on earth has a different chemical
  composition (H2O) to “water on twin earth
• If we assumed that meaning was “in our
  heads”, then “water” would mean the same
  thing on earth and twin earth.

• But it doesn’t, since our “water” means H O  2
  and their “water” means XYZ.

• So what we really mean when we use the
  word “water” is the objective nature of the
  thing (even if we don’t know this)

• This is similar to Aristotle’s view (cf. whales)

• Kripke argued that statements like “Water is
  H2O” are necessary truths, even though they
  are not a priori.
• If “Socrates” really means something like the
  description “the teacher of Plato” to a
  person (Russell), then they mean the same
  thing to that person.
• But what if Socrates had died young? That
  might have happened.

• Then, if “the teacher of Plato” is synonymous
  with “Socrates”, someone else could have
  become Socrates.

• But that is absurd, only Socrates was
  Socrates, whatever descriptions are true of
  him (or not).

• Kripke: “Socrates” is a rigid designator
• It is not logically possible for a rigid
  designator to refer to anything else (unlike
  non-rigid designators like “the teacher of

• So, on Kripke’s view, the way in which we
  think about things (sense) does not have
  anything to do with the meaning of names
  like “Socrates”.

• Kripke: natural kind terms are rigid
•   “Water” and “H2O” refer to the same object in
    the world. Both designate rigidly.

•   Thus it could never be true that these terms
    referred to different entities.

•   So “Water is H2O” is necessarily true, (whether
    we know it or not) even though this is not an a
    priori truth (it is a truth about the world, not
    about our concepts)

•   This is pretty much the same as Aristotle’s view.
    Being H2O is the objective essence of water, and
    this is not changed by our use of words.

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