LOGIC AND CRITICAL THINKING

DEFINITION AND SCOPE OF PHILOSOPHY

Whenever a question such as what is philosophy? is asked, no straightforward answer can be

given. Because of the complex nature of the discipline it is not easy to define philosophy in a

way acceptable to every philosopher. For instance, it is easy to ask a student of biology or

physics what the definition of their respective disciplines are and get a straight forward answer.

But this is not possible with philosophy. Philosophy as a discipline does not have a universal

definition. So the first problem a student of philosophy encounters is that of the definition of

philosophy. Philosophers do not agree among themselves on what philosophy is. Either they run

away from defining the subject or they mostly do so according to their various schools of

thought, culture and even tradition. That is why for most introductory textbooks on philosophy,

the best way to define philosophy is to do philosophy, (Popkin 1982). In the absence of a

universal definition or understanding of philosophy, the discipline has been given various

meanings and definitions.

To the average man-in-the street, philosophy is used first to mean “an attitude towards a certain

line of action”, a ‘general view of life or a general theory or principles about how we ought to

conduct our lives” (Halverson, 1967: 4). the professional philosopher begins to define

philosophy from its origin. According to academic philosophers, philosophy originated from the

Ancient Greek City State of Miletus. This was around the late 5th and early 6th century B.C. But

you should also quickly remember that this Eurocentric view which limits the Origin of

Philosophy to the Ancient Greeks has been criticized and rejected by some contemporary

African philosophers. To some African Philosophers such as Eboussi Boulaga, Marcien Towa, E.
Njoh Mouelle and P.O. Bodunrin, philosophy also has an African origin. There existed early

intellectual, scientific and philosophical activities in Ancient Africa long before their European

or Western counterparts began any meaningful philosophical inquiry. It is on record that Ionian

Philosophers especially Pythagoras and Thales visited Africa notably Ancient Egypt and “were

educated in all disciplines of knowledge by African teachers.

Ancient Greece remains the first place in Europe where philosophy was systematized as a

discipline. Pythagoras was the first to make a standard comment about the nature and definition

of philosophy. He was a Greek mystic, mathematician and philosopher. It is on record that

“when he was called Wise man, he said that his wisdom only consisted in knowing that he was

ignorant and that he should therefore not be called a wise man but a “lover of wisdom”

BRANCHES OF PHILOSOPHY

This section introduces you to the major branches of philosophy. It is an opportunity for you to

know the divisions and sub-divisions within philosophy.

Logic

Etymologically, logic as a discipline derives from the Greek word Logos, which means study,

word or discourse You should always remember that whenever a question such as what is logic

is asked no straight forward answer can be given. Logic has been variously defined by different

scholars. Copi for instance, defines “logic as the study of the methods and principles used in

distinguishing good (correct) from bad (incorrect) reasoning” (1972). On the other hand, Nancy

sees Logic “as the science that appraises reasoning as correct or incorrect” (1990:34). Kahane on

his part defines logic as “an attempt to distinguish between correct (valid) and incorrect (invalid)

arguments” (1968:2). Logic can also be defined as the science of good or bad reasoning.
METAPHYSICS

Etymologically, the word metaphysics came from two Greek words META which means “after”

and PHYSIKA which means “Physics” or “nature”. So the Greek word METAPHYSIKA means

“after the things of nature or after physics.

Unlike logic, metaphysics is the study of the “first principle” or ultimate reality. It is also called

the theory of Being. It is the only science that deals with the study of the basic and fundamental

issues of the universe. In his view, metaphysics studies the totality of things in the universe both

the possible and the real, the visible and the invisible. Metaphysics is a general study of existence

and reality.

Epistemology

Epistemology is one of the most important branches of philosophy Etymologically, it derives

from two Greek words “Episteme” which means “knowledge” and “logos”. which means “study,

discourse or reasoning” Epistemology is best known as the branch of critical philosophy which

consists in investigating the scope, source and limitations of human knowledge. Epistemology

tries to discover what knowledge is and how it differs from mere opinion or belief. That is why it

is also called theory of knowledge. According to Aristotle, “every man wants to know,” and this

is very relevant to man’s life.

Ethics

Ethics is mostly known as “the branch of philosophy which deals with the morality of human

actions in society” (Omoregbe, 1989:2). Etymologically ethics comes from the Greek word

“Ethos” which means “custom” or “character”. Sometimes it is called “moral philosophy”. And
you should always remember that Socrates was the first to systematize the discipline. He was the

first to claim that “the unexamined life is not worth living”.

SOURCES OF KNOWLEDGE AND CRITERIA FOR KNOWING

There are different sources and criteria for knowing. It is an opportunity for you to differentiate

between common sense and philosophical understanding of knowledge, belief and opinion.

Difference between Knowledge, Opinion and Belief

In ordinary language it seems there is no difference, at all, between knowledge, opinion and

belief. Often times, they are used interchangeably.

The philosophical understanding of knowledge is very different from that of the layman. For a

layman, knowledge, opinion and belief are interwoven. But it is not possible in philosophy. For a

philosopher, you say “know” when you possess information that is beyond doubt. Philosophical

knowledge follows the logic of proposition. i.e. “I know that…” for example, “I know that

Liberia is the oldest Republic in Africa”. “I know that Liberia and Sierra Leone are neighbors.

What matters here is that knowledge implies being sure, being certain. Also believing can be

seen as a pre-condition for knowledge. Because when you know something, you have a right to a

certain confidence in your belief as a true and reliable guide to action.

Therefore, they do not constitute knowledge. Always remember that the knower must not only be

able to adduce sufficient evidence but must also know that he knows his beliefs. For to know is

to know that you know. It must be clear to you now that knowledge is quite different from

opinion or belief. We have knowledge only when we can provide reasons and evidence for our

claims. On the contrary, belief or opinion is based on inner, personal certainty and conviction.

Knowledge is objective i.e. it must be communicable and verifiable.

knowledge come about? How do we know propositions to be true? Or by what means do we

come by our knowledge of the real world? Answers to these questions have been given through

the following means: (a) Reason, (b) Sense experience (c) Authority (d) Intuition (e)

Revelation/faith and (f) Mystical experience.

Reason

Rationalism in the theory which believes that human beings can acquire knowledge of reality by

the use of our minds alone, by thinking or pure reason. To any rationalist, reason is a necessary

ingredient for all our knowledge claims. This is one of the reasons why Aristotle defines man as

“a rational animal”. Thus, the ability to think is what is called reason.

Sense Experience/Empiricism

Sense experience is another source of knowledge. Empiricists are the proponents of sense

experience theory. To any empiricist, as far as knowledge is concerned, only sense experience

matters. In other words, empiricism is the philosophical theory which denies reason while

insisting that experience is always the necessary ingredient in our knowledge claims of the

natural world.

Authority

Authority is also considered as one of the sources of knowledge. Authority as source of

knowledge occurs when we make certain claims to knowledge based on the authority of someone

who is a specialist in the particular field of knowledge. “Magister dixit” i.e. the ‘Master said”.
Revelation and Faith

These are also considered as sources of knowledge. It is common to hear people: “it was

revealed to me in a dream” or “it was revealed to me by God and I have faith in it”. “My faith

guides me in this matter and I know that it is certainly true

Perception

Our senses (sight, hearing, touch, taste, smell) provide direct experiences and observations of the

world around us. This kind of knowledge is based on empirical evidence, like seeing or hearing

something firsthand.

Testimony

Knowledge gained from others through communication, such as books, articles, teachers, or

peers. This relies on the trustworthiness of the source and can be passed down from one

generation to another.

Intuition

Sometimes, knowledge comes from a "gut feeling" or instinct, a deep sense of understanding that

doesn’t necessarily rely on conscious reasoning. This type of knowledge is often used in creative

or abstract thinking.

DEFINITION AND SCOPE OF LOGIC

Unlike philosophy itself, logicians seem to agree on what logic means or what it is about. Logic

has been variously defined by different scholars. For instance, Copi defines logic as the study of

the methods and principles used in distinguishing good (correct) from bad /incorrect reasoning
(1972). On the other hand, Nancy sees logic “as the science that appraises reasoning as correct or

incorrect” (1990:3.4). Kahane on his part defines logic as “an attempt to distinguish between

correct (valid) from incorrect (invalid) arguments” (1968:2). Etymologically, Logic is derived

from Greek Word Logos, which means study, word or discourse. Basically, you can notice that

in the above definitions the words which stand out clearly are reasoning and argumentation.

Therefore, we can say that the study of logic is the study of correct and incorrect reasoning and

arguments.

Why Study Logic?

It is very important to study logic. Because it is the only discipline that strictly lays down the

rules which the mind must follow in order to arrive at truth and thereby minimize error. In other

words, logic is the only discipline that teaches us how to formulate different types of arguments.

As a discipline it will also equip you with the skills needed for effective and forceful presentation

of your views in an argument. Logic is sometimes perceived by its critics as a subject that has no

practical use. This is not true. The abstractness of logic does not make it irrelevant at all. Indeed,

it is not contradictory to say that logic is to life what oxygen is to life. We all need logic in one

way or the other, in one form or another. We all need logic to communicate and interact in the

society.

Logical Processes

Logical processes include:

Simple apprehension

Judgment
Reasoning and Argument

Simple Apprehension

Simple apprehension is the act by which the mind forms the concept of something without

affirming or denying anything about it. For instance, if I say “look at that Ship” and stop there.

This is a simple apprehension because I have not said anything about the Ship. I have neither

affirmed nor denied anything about the Ship. Some philosophers and logicians have denied the

possibility of a simple apprehension. According to them, there is nothing like simple

apprehension.

Judgment

In logic, judgment is known as the act by which the mind affirms or denies something of

something else. For instance, if I proceed to say “look, that ship is big” then I have made a

judgment by affirming the

“bigness” of the Ship

Reasoning and Argument

Reasoning and argument constitutes the third and last stage of any logical process. It is also

known as the act by which the mind passes from one, two or more judgments to a further

judgment distinct from the preceding ones but implicitly contained in them. Besides simple

apprehension and judgment, logic is strictly concerned with reasoning and argument.

LOGIC’S VOCABULARY
Statement and Proposition

There is no difference between a statement and a proposition in logic. The two terms are

synonymous and thereupon interchangeable. However, logicians differentiate between statement

and sentence. To them, even though the two terms are interwoven, they are not actually the same.

For instance, in everyday English, a sentence is a set of words expressing a statement, a question

or a command. Thus whenever a sentence expresses a statement without question or command it

can also be called logical statement. It should also be clear to you that in ordinary English, every

logical statement is a sentence. But as stated earlier not every sentence is a logical statement. It is

only when a sentence can both be denied or asserted that is qualified as logical statement or

proposition. For example, the sentence “Liberia is rich” can be asserted as follows: yes, Liberia

is rich. It can also be denied by stating as follows: No, Liberia is not poor. Thus the sentence

“Liberia is poor” because it can be asserted and can also be denied, is a logical statement or

proposition. Any sentence expressing questions, commands etc does not qualify as logical

statement or proposition.

Premise

Premise is also one of the basic concepts in logic. It is known as evidence. Basically, a premise

refers to that proposition or statement, within an argument, which provides support for or

grounds for asserting the conclusion of that argument. (Meneye Eze, 2003). In a valid argument,

the premises imply the conclusion.

Premise and conclusion are relative terms. Conclusion does not necessarily mean the last

sentence. The premise in an argument A can be the conclusion in argument B and vice- versa.

All men are mortal

Therefore, Adama is a man.

In this example, the first two statements or prepositions are the premises while the last one is the

conclusion.

All philosophy students are wise

Esther Omowole is a philosophy student

Therefore, Esther Omowole is wise

Here, it is clear that the third preposition “Esther Omowole is wise”, which is the conclusion of

the argument, is arrived at on the basis of the information provided by the first two prepositions,

which are the premises.

Inference

In logic to infer means to derive the conclusion of an argument from the premises of that

argument. For example:

All Liberians are affectionate

Adasa F. Gross is a Liberian

Therefore, Adasa is affectionate

Here you can see that the conclusion “Adasa is affectionate” is derived from the first and second

premises of the argument. This process of derivation is called inference.

An argument is a group of propositions, one of which, called the conclusion, is affirmed on the

basis of the others, which are called premises. An argument is always the smallest unit of

argumentation. At least two propositions or statements form an argument otherwise it is not

argument. But not all the statements are arguments. Some non-argumentative uses of statements

such as in reports, illustration, explanatory statements, conditional statement etc…are sometimes

confused with arguments. As earlier stated, at least two statements or propositions form an

argument. In the case of two propositions only one must be the premise while the other must be

the conclusion.

For instance: “As soon as Adama comes, he marks his scripts.” Here the conclusion is “he marks

his scripts” while the premise is “Adama comes”. The expression “as soon as” stands as premise

– indicator. When more than two propositions or statements form an argument, one must be a

conclusion while the others must be premises

Example: All Students are studious

Massa Gross is a Student

Therefore, Massa Gross is studious

You should always remember that no matter how many premises form an argument; an argument

can never have more than one conclusion.

Valid and Invalid Arguments

An argument is said to be valid when the conclusion of that argument is derived from or follows

from the premises. In other words, in a valid argument, it is necessary that if the premises are
 true, then the conclusion is true. Thus, in any valid argument, there is an absolute connection

between the premises and the conclusion. In any valid argument, it is impossible for the

conclusion to be false when the premises are true, for example:

All AUWA lecturers are brilliant

Uriah Bailey is a lecturer of AWUA

Therefore, Uriah Bailey is brilliant.

 All numbers ending in 0 or 5 are divisible by 5. The number 35 ends with a 5,

 All birds have feathers. All robins are birds. Therefore, robins have feathers.

 It's dangerous to drive on icy streets. The streets are icy now, so it would be
dangerous to drive on the streets.

 All cats have a keen sense of smell. Fluffy is a cat, so Fluffy has a keen sense
of smell.

 Cacti are plants, and all plants perform photosynthesis. Therefore, cacti
perform photosynthesis.

 Red meat has iron in it, and beef is red meat. Therefore, beef has iron in it.

 Acute angles are less than 90 degrees. This angle is 40 degrees, so it must
be an acute angle.

 All noble gases are stable. Helium is a noble gas, so helium is stable.

 Elephants have cells in their bodies, and all cells have DNA. Therefore,
elephants have DNA.

 All horses have manes. The Arabian is a horse; therefore, Arabians have
manes.
 What matters most here is the link between the premises and the conclusion rather than on the

truth or falsity of the statements comprising the arguments.

Example: All birds have beaks.

Some cats are birds.

So, some cats have beaks.

 All swans are white. Jane is white. Therefore, Jane is a swan.

 All farmers like burgers. Jethro likes chicken wings. Therefore, Jethro is not a
farmer.

 All actors are handsome. Tom Cruise is handsome. Therefore, Tom Cruise is
an actor

Here you can see that although the second premise is false, the argument is still valid. Because

when the premises are assumed to be true the conclusion must be true also.

In logic proper, an argument can still be valid when all the premises are false.

For example: All men are monkeys.

All monkeys are politicians.

So all men are politician.

However, it is not also advisable to hastily conclude that an argument is valid simply because its

premises are all true.

Example: Some Liberians are bad.

Peter is a Liberian.
Therefore, Peter is bad.

An argument can have true premises and true conclusion but may not necessarily be valid.

Because sometimes, the premises may not support the conclusion in the right way.

“Are the premises actually true?” “Is the argument valid?” These are two distinct and

fundamental questions in logic. In logic proper, validity only preserves truth but cannot preserve

falsehood.

An invalid argument is the opposite of valid one. But invalid argument has a peculiar

characteristic: for instance: it is not necessary that if the premises are true, then the conclusion is

true.

In conclusion, any valid argument with all premises true is a sound argument. Any valid

argument with at least one false premise in an unsound argument. All invalid arguments are

unsound.

Inductive argument

An inductive argument is that kind of argument that proceeds from the experienced (particular)

to the inexperienced (general); from the known to the unknown.

For instance

H.E. Roger Miller is a Cameroonian and a football player.

Mr. Etoo Fils is a Cameroonian and a football player.

Mr. Rigobert Song is a Cameroonian and a football player.

Therefore, All Cameroonians are football players.

(general proposition) is arrived at by sampling some members of the class of persons who are

Cameroonians. But for some logicians (Minimah & Inoka, 1997) there are also some “cases in

which the propositions of an inductive argument which are used as premises and conclusions

may all be either general propositions or particular prepositions”. This is evident in the following

arguments:

a) All birds grow from infancy to adulthood;

All trees grow from infancy to maturity;

All men grow from infancy to adulthood;

Therefore, all living things grow infancy to adulthood

Idi Amin was a dictator and was ruthless;

Samuel Doe was a dictator and was ruthless;

Kabila is a dictator,

Therefore, Kabila is ruthless

Inductive Reasoning: The first lipstick I pulled from my bag is red. The second lipstick I pulled
from my bag is red. Therefore, all the lipsticks in my bag are red.
Deductive Reasoning: The first lipstick I pulled from my bag is red. All lipsticks in my bag are
red. Therefore, the second lipstick I pull from my bag will be red, too.
Inductive Reasoning: My mother is Irish. She has blond hair. Therefore, everyone from Ireland
has blond hair.
Deductive Reasoning: Everyone from Ireland has blond hair. My mother is Irish. Therefore, my
mother has blond hair.
Inductive Reasoning: Poor no Friend is a shelter dog. He is happy. All shelter dogs are happy.
Deductive Reasoning: All shelter dogs are happy. Poor no Friend is a shelter dog. Therefore, he
is happy.
Weak and strong inductive arguments

As noted earlier, valid or invalid are words reserved for arguments only while ‘weak’ or ‘strong’

are used to qualify inductive arguments. As stated earlier, on inductive argument is based on

probability. That is why logicians rather use the words weak and strong. In an inductive

argument, the words strong and weak are used to indicate the level and strength of evidence or

data used as premises and the degree of certainty contained in the conclusion. Any inductive

argument is based on probability. Therefore, its weakness or strength depends on the degree of

evidence contained in the conclusion.

Deductive Argument

Logicians define deductive argument as that kind of argument in which we move from general

propositions as premises to a particular proposition as the conclusion. In a deductive argument

the derivation of a conclusion from the premises follows with absolute certainty and necessity,

no matter what. But this is not the case in an inductive argument. For instance:

All men are mortal

Aristotle is a man

Therefore, Aristotle is mortal.

Valid (deductive) argument

For a deductive argument to be valid at least the following conditions must be fulfilled. In other

words, a deductive argument is valid if only if:

a) The premises imply the conclusion; or

c) The conclusion follows from the premises, or

d) The premises necessitate the conclusion, or

e) The conclusion can be inferred from the premises.

You can see that from the above conditions, a valid deductive argument is an argument in which

the conclusion is implied by or is entailed by, or is necessitated by the premises or the premises

are followed by the conclusion. You should also know that in logic proper, the words “true” or

“false” are used to qualify statements or propositions. While “valid” or “invalid” are used to

qualify arguments. In other words, we talk of “true” or “false” statements or propositions and

“valid” or “invalid” arguments.

Sound and Unsound Argument

First of all, the words “sound” and “unsound” have nothing to do with an invalid argument. They

are only used to qualify a valid (deductive) argument. Also bear in mind that before an argument

becomes sound or unsound it must be valid beforehand. Thus a valid argument is said to be

sound if the premises of that argument as well as the conclusion are all true prepositions. On

other hand, a valid argument is said to be unsound if the premises of that argument are either all

false or contain a mixture of true and false prepositions, notwithstanding the truth value of its

conclusion (Minimah and Inoka, 1997:74).

Therefore, as stated earlier, the words sound and unsound only serve to show the truth value of

the premises contained in any argument.

All Liberian are saints

All saints are angels

Therefore, all Liberian are angels

b) All Liberian are Africans

All Africans are whites

Therefore, all Liberian are whites

You can see that in example (a), both the two premises plus the conclusion are false propositions

yet the argument is valid, because the conclusion necessarily follows from the premises. Again,

in example (b), the first premises have a true proposition, the second has a false proposition,

while the conclusion is also expressed in a false proposition. But here again, the argument is

valid because despite the falsity of the second premise and the falsity of the conclusion, the

conclusion is validly derived from the combination of the false and true premises. So in both

examples (a) and (b), the arguments are valid but unsound. Unsound in the sense that the valid

argument has false premise and false conclusion (a), and one true premises and one false premise

with a false conclusion (b). Where a valid argument has all its premises and conclusion as true

propositions, then that valid argument is also a sound argument. However, you should always

bear in mind that the fact that an argument has all its premises true does not necessarily mean

that it must be valid. It is possible to an argument to remain invalid even if all its premises are

true.

For example: All boys are dressed in shirts

Therefore, some girls are boys

Thus any argument in which all the premises are true but has the conclusion as false preposition

must be an invalid argument.