Tuesday, July 22, 2014

Logic Lessons Pt 12 - Kinds of Definitions

Once we have established the rules for definitions, it important to list the kinds of definitions.

1.  Nominal.
     This is a definition of a word rather than the thing that the word designates.  This means that it the definition is in reference to how a word is used rather than what it is.  A nominal definition is something that Webster is interested in when giving the different ways that word "soul" is used in the English language.  But a real definition is what Plato is interested in when asking question in through his dialogues to discover what is the soul's essence.

Nominal definitions are not true or false.  It is simply a matter of their usage.

Of nominal definitions, they are men to convey
a. Conventional Meanings - this refers what is commonly held as the definition, whether or not it is accurate.  The conventional meaning of "education" is schooling by teachers over students.  But the thing itself is not limited to that.
b.  Specialized Meanings - this refers to definitions agreed upon in a discussion.  For example, if you are trying to define human life, you can say, "Let's stipulate that any creature that has reason is human."  And if you and your interlocutor agree, it is a specialized meaning.
c.  Synonym.  - this is the simple word replacement for an equivalent word.
d.  Etymology - understanding the word's origin as definition.  For example "philosophy" is based on two Greek words "phileo" meaning "love" and "sophia" meaning wisdom."  So philosophy is the "love of wisdom."
e. Examples - These are not strictly definitions but they are helpful to get the idea across to someone.  Try defining the color red.  You'll find t"3-hat more often than anything, you point out red things rather than define the thing itself.

2.  Essential
     This should give the genus and specific difference (or property) of the thing being defined.  This is what Socrates always strove for.  He wanted to understand a thing's essence.

When using a genus, you should use the narrowest of genus available.  You could use the genus "shape" or "plane figure" for "triangle."  "Plane figure" is a narrower genus and so it is preferable.

The specific difference tells us how the thing being defined is different than all the other things in the genus.  "3-Sided, enclosed, whose angles equal 180 degrees" is the specific difference.

Together, the genus and specific difference gives us the species.

For example, the species of human is the animal (genus) that is rational (specific difference).  We are like all the other beasts because we share the fact that we are all animals.  But we are different because we are the only ones who have reason.

3.  By Property.
  This is a quality that flows from the essence.  For example, if you said that "Humans are animals that write poetry," you are defining "humans" by a quality that comes only from its essence.  Since the essence of human beings is that we are rational and only those who have reason have language and only those who have language have poetry, therefore human beings are the animals that write poetry."

4.  By Accidents.
   Accidental properties are changeable, non-essential aspects of a thing.  You could define the "clouds" to a child as "the white things in the sky."  But those qualities of "whiteness" and "in-the-skyness" are not essential to a cloud.  Clouds can be different colors.  They can also be be in other locations.  But even though accidents cannot give you an essential definition, if you add enough of them you can convey a clear picture of the subject another person.

5.  By Efficient Cause.
  This is the an explanation of a things origins.  E.g. "AIDS is a disease caused by HIV."

6.  By Final Cause.
  This defining a thing by the purpose for which it is designed.  E.g. "A pen is an instrument for writing."

7. From  Material Cause
  This is defining a thing by its composition.  E.g. "Water is 2 parts hydrogen and 1 part oxygen."

8.  From Effects.
   This is usually done as a catch-all for something that cannot be defined in any other way than the effect it causes.  E.g. a "carcinogen" is defined as "anything the causes cancer."

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