CRITICAL THINKING
THE TWO FORMS OF CRITICAL THINKING THAT WE USE
DAILY ARE INDUCTIVE AND DEDUCTIVE REASONING.
INDUCTIVE
DEDUCTIVE
PATH OF
ARGUMENT
SPECIFIC TO
GENERAL
CONCLUSION
FIND A
PROBABILITY
FIND A
CERTAINTY
DISCOVER
SOMETHING NEW
APPLY WHAT
IS KNOWN
USED TO
COMMONLY
USED IN
RESEARCH, SUCH
AS MEDICAL OR
TECHNICAL RESEARCH
GENERAL TO
SPECIFIC
STRENGTHEN
OR CONFIRM
ARGUMENTS
INDUCTIVE EXAMPLE: YOU PURCHASE A CHRYSLER VEHICLE AND FIND IT IS
EXCELLENT. SEVERAL PEOPLE YOU KNOW ALSO HAVE EXCELLENT
CHRYSLER VEHICLES. YOU CONCLUDE THAT CHRYSLER PRODUCTS ARE
EXCELLENT PRODUCTS.
DEDUCTIVE EXAMPLE: YOU HAVE BEEN TESTED FOR ALLERGIES, ALL SORTS
POSSIBLE, AND FIND THAT THE ONLY THING IN THE WORLD THAT YOU ARE
ALLERGIC TO IS CATS. YOU GO TO A FRIEND’S HOME AND BEFORE LONG
BEGIN TO DISPLAY ALL THE SYMPTOMS OF AN ALLERGY ATTACK. THE
CONCLUSION IS THAT YOUR FRIEND HAS A CAT.
SYLLOGISM
THE MOST COMMON EVERYDAY TYPE OF LOGICAL REASONING FOR
ARGUMENT IS DEDUCTIVE. THE PRIMARY FORM OF DEDUCTIVE REASONING
IS CALLED SYLLOGISM.
WHILE SYLLOGISTIC REASONING HAS PROGRESSIVELY MORE COMPLEX
STRUCTURES, THE BASIC FORM IS SIMPLE AND STRAIGHT-FORWARD AND
CAN BE LIKENED TO AN EQUATION:
MAJOR PREMISE: QUALIFIED AND ABSOLUTE; A BROAD STATEMENT
A=B
MINOR PREMISE: A NARROW STATEMENT RELATED TO THE MAJOR PREMISE
C=A
CONCLUSION: MUST FOLLOW LOGICALLY FROM THE PREMISES
C=B
THE CLASSIC EXAMPLE:
MAJOR PREMISE: ALL MEN ARE MORTAL.
MINOR PREMISE: GEORGE IS A MAN.
CONCLUSION: GEORGE IS MORTAL.
BEWARE THE DIFFERENCE BETWEEN VALID/INVALID AND TRUE/FALSE:
VALID/INVALID REFERS ONLY TO STRUCTURE; IF THE STRUCTURE IS
CORRECTLY MADE, THE SYLLOGISM IS VALID. IF THE STRUCTURE IS NOT
CORRECT, THE SYLLOGISM IS INVALID. THIS HAS NOTHING WHATSOEVER TO
DO WITH TRUE/FALSE.
TRUE/FALSE REFERS ONLY TO CONTENT, THAT IS, WHETHER THE
STATEMENTS AND CONCLUSION ARE TRUE AND THEREFORE LOGICAL.
HOW TO DETERMINE IF A CONCLUSION IS TRUE OR FALSE: IF (1) THE MAJOR
PREMISE IS TRUE, (2) THE MINOR PREMISE IS TRUE, AND (3) THE
STRUCTURE IS VALID, THE CONCLUSION MUST BE TRUE.
IF ONE OR BOTH OF THE PREMISES ARE FALSE, THE CONCLUSION IS
USUALLY FALSE, EVEN THOUGH THE STRUCTURE IS VALID. SOMETIMES,
DEPENDING ON THE ELEMENTS, A CONCLUSION IS TRUE EVEN THOUGH THE
STRUCTURE IS INVALID. HOWEVER, YOU CANNOT DEPEND ON THE
CONCLUSION BEING TRUE IF THE STATEMENT IS NOT VALID.
IT WILL SIMPLY BE A FLUKE, NOT A RULE OF PROBABILITY.
TEST FOR VALIDITY AS WELL AS TRUE PREMISES.
BEWARE OF UNSTATED ASSUMPTIONS. THEY MUST BE CHALLENGED BY
STATING THEM AND CHECKING TO DETERMINE IF THEY ARE TRUE.
EXAMPLE #1: THE ASSUMPTION THAT SOMETHING IS TRUE BECAUSE IT WAS
IN THE NEWSPAPER LIES ON THE UNSTATED ASSUMPTION THAT EVERYTHING
IN THE NEWSPAPERS IS CORRECT.
EXAMPLE #2: A CORPORATION’S CLAIM THAT IT SHOULD NOT BE REQUIRED
TO INSTALL POLLUTION CONTROLS BECAUSE IT WOULD EAT INTO THE
PROFITS RESTS ON THE UNSTATED ASSUMPTION THAT COMPANIES SHOULD
NEVER DO ANYTHING TO LOWER PROFITS.
EXAMPLE #3: THE BELIEF THAT STUDENTS SHOULD NEVER QUESTION WHAT
HE/SHE IS TOLD BY A TEACHER STEMS FROM THE BELIEF THAT TEACHERS
KNOW IT AND STUDENTS MUST ABSORB IT, AND THAT TEACHERS WILL
NEVER TELL A LIE OR GIVE AN OPINION AS FACT.
EXAMPLE #4: THE ACCEPTED BELIEF THAT ALL GOVERNMENT AND
POLITICIANS ARE CORRUPT AND THAT CITIZENS ARE LOSING THEIR RIGHTS
HAS FLOWERED OUT OF THE PERCEIVED LOSS OF RIGHTS AS UNPOPULAR
LAWS ARE PASSED AND THE PUBLICITY GIVEN THOSE POLITICIANS WHO
STUMBLE.