Classification and Definition
Morris Cohen and Ernest Nagel
An Introduction to logic and scientific method, pp. 223 - 231
©Harcourt, Brace & World, Inc. 1934
Copyright, 1996 © Dale Carnegie & Associates, Inc.
Natural and Artificial Classes
• “Natural” classes
– classifying traits according to facts
• “Artificial” classes
– classifying traits through arbitrary selection
Natural and Artificial Classes
• “Artificial” classes aren’t artificial at all?
• All classes are artificial?
The Significance of
Classification
• Classification is useful as a principle of
organizing knowledge
• It should be determined by traits that have
the highest logical value
– i.e. whale = classified with pickerel or with
horse?
Summary of Classification
• Science is supposed to gather facts, then
classify them
• We often have to classify items before we
can determine how to gather facts about
them.
Conclusion of Classification
• Traits should be classified according to the
most significant information about an item’s
nature
• Who are qualified to make these decision?
– Experts
– Formal logic
The Purpose of Definition
• Psychological motivation
– desire to learn the meanings of new words
– desire to economize speech
– desire to understand a word’s meaning better
• To produce accurate thinking and
communication by reducing vagueness and
ambiguity in language use
The Nature of Definition
• Vagueness
– problems with shared denotations
• i.e., “genius” =
– Isaac Newton, for his contributions to physics
– any person with a high IQ
– a baby to his mother
– nonspecific, needs context
• i.e., “there’s moss on the log” (Linguistics 401, Dr. Andrea
Wilhelm, January 2005)
– …on top of the log.
– …on the side of the log.
– …on the back of the log.
The Nature of Definition
• Ambiguity
– One word, two meanings
• i.e., “desirable” - John Stuart Mills (225)
– attractive (desirable woman)
– worth seeking (desirable legislation)
– One phrase, two meanings
• i.e., “Lisa met the new French teacher” (Linguistics 401,
Dr. Andrea Wilhelm, January 2005)
– …the new teacher from France.
– …the new teacher of French.
Nominal Definition
• Agreement or resolution regarding the use
of verbal symbols (228)
– Definiendum - new symbol to replace known
symbol/word (definiens)
• i.e., Algebraic exponents: a2 = a . a. Df.
Nominal Definition
• Neither true nor false
• Not a proposition
• Aids in scientific inquiry
– It economizes language use
– It adds clarity
Definition by Denotation
• Dictionary meaning / real-world symbol
• Core information that fixes/symbolizes
reference (224)
– i.e. ‘city’ denotes individual places such as
Edmonton.
– i.e., M. Jourdain uses specific examples to
denote prose (226)
Definition by Denotation
• A symbolic representation of a word form is
not a definition
– i.e., Euthyphro’s definition of ‘piety’ (227)
Real Definition
• Analysis of the symbolized reference
• Genuine and universal proposition
– may be either true or false
• i.e., Euthyphro’s second attempt at defining piety
– Piety. = . that which is dear to the gods. Df. (230)