1. Logic and Legal Profession
Beginning of Professionalism
Vijay Pd. Jayshwal
Kathmandu School of Law
2. Logic Stands for………..
• Logic is the use and study of valid reasoning. The study of
logic features most prominently in the subjects of
philosophy, mathematics, and computer science.
• Logic was studied in several ancient civilizations, including
India (Hindu Philosophy), China (Confucius philosophy ),
Persia (Persian Logic) and Greece. In the West, logic was
established as a formal discipline by Aristotle, who gave it a
fundamental place in “philosophy.”
• In the East, logic was developed by Buddhists and Jains.
• It is the process of finding the valid reasoning through
scientific methods which includes the proper evidence and
established principle applicable world widely.
3. Philosophy ???
• The word ‘philosophy’ is derived from the ancient
Greek term philosophia, literally meaning the
‘love of wisdom’ (philein = to love + sophia =
wisdom) in the sense of theoretical or cosmic
• In Sanskrit language, this is darsan, literally
meaning to make something revealed or obvious
by process of investigation.
• Both indicate to ‘knowledge of ideas’. The
method of Philosophy is scientific.
4. Logic Definitions in words of Jurist:-
1. The tool for distinguishing between the true and the false (Averroes).
2. The science of reasoning, teaching the way of investigating unknown
truth in connection with a thesis (Robert Kilwardby).
3. The art whose function is to direct the reason lest it err in the
manner of inferring or knowing (John Poinsot).
4. The art of conducting reason well in knowing things (Antoine
5. The right use of reason in the inquiry after truth (Isaac Watts).
6. The Science, as well as the Art, of reasoning (Richard Whately).
7. The science of the operations of the understanding which are
subservient to the estimation of evidence (John Stuart Mill).
8. The science of the laws of discursive thought (James McCosh).
9. The science of the most general laws of truth (Gottlob Frege).
10. The science which directs the operations of the mind in the
attainment of truth (George Hayward Joyce).
11. The branch of philosophy concerned with analyzing the patterns of
reasoning by which a conclusion is drawn from a set of premisses
(Collins English Dictionary)
12. The formal systematic study of the principles of valid inference and
correct reasoning (Penguin Encyclopedia).
5. The study of the standards of correct argumentation.
The characteristic method of this study is the
development of formal logic to symbolize and evaluate
Logics can be divided into three models
1. Propositional logic: the logic of simple
indicative statements- categorical reasoning by
2. Modal logic: deals with logical relationship
involved in particular aspects of the language-
such as modal qualifiers like ‘possibly’ and
3. Temporal Logic: It deals with the logical
relationship established by tense of a ‘sentence
Bertrand Russell: “Science is what we know and
philosophy is what we don’t know”
Ludwig Wittgenstein: What is your aim in
philosophy? To show the fly the way out of
the –fly bottle.
Ambrose Bierce: A route of many roads
leading from nowhere to nothing.
• Reasoning is the act of ‘using reason to derive
a conclusion from certain premise. Reasoning
‘provides’ justification for belief to ‘be true’.
Obviously, reasoning is a ‘foundation of truth’.
• In general, a distinction is made between
reasoning from the general to the particular (
called deductive reasoning) and
reasoning from the particular to the general
• Reasoning is a special mental
activity called inferring, what
can also be called making (or
performing) inferences (To
infer is to draw conclusions
from premises) Like:-
• You see smoke and infer that
there is a fire.
• You count 19 persons in a
group that originally had 20,
and you infer that someone is
• The reasoning process may
be thought of as beginning
with input (premises, data,
etc.) and producing output
(conclusions). In each specific
case of drawing (inferring) a
conclusion C from premises
P1, P2, P3, ..., the details of
the actual mental process
(how the "gears" work) is not
the proper concern of logic,
but of psychology or
neurophysiology. The proper
concern of logic is whether
the inference of C on the
basis of P1, P2, P3, ... is
9. • Inferences are made on the basis of various
sorts of things – data, facts, information,
states of affairs. In order to simplify the
investigation of reasoning, logic treats all of
these things in terms of a single sort of thing –
statements. (A statement is a declarative sentence, which is to
say a sentence that is capable of being true or false.)
it is raining, I am hungry, 2+2 = 4, and others God exists
Logic correspondingly treats inferences in terms of collections of
statements, which are called arguments. The word ‘argument’
has a number of meanings in ordinary English.
An argument is a collection of statements, one of
which is designated as the conclusion, and the
remainder of which are designated as the premises
10. Pictorial Representation of
There is smoke (premise)
there fore, there is fire
THERE were 20
there are 19
11. Deductive Reasoning
• When Snow Falls, the Forests Get
• White. This Year
• There is Plenty
• of Snow Fall in Phulchoki.
• the Forest in Phulchoki has
• become White
General to Particular:
Logic is a method of
reaching a new
truth out of given premises
by valid reasoning
(Inductive reasoning is s
process of making a
general conclusion out of
(Deductive reasoning is
process of reaching a
conclusion by the
application of general
law to specific case)
14. Inductive Reasoning:
Dog 1 has four legs.
Dog 2 has four legs.
Dog 2 has four legs.
Dog 2 has four legs.
Dog 2 has four legs.
Dog n has four legs.
All dogs have four legs.
16. •Jill and Bob are friends. Jill likes to dance, cook and write. Bob
likes to dance and cook. Therefore it can be assumed he also likes
•Jennifer leaves for school at 7:00 a.m. and is on time. Jennifer
assumes, then, that she will always be on time if she leaves at 7:00
•Robert is a teacher. All teachers are nice. Therefore, it can be
assumed that Robert is nice.
•All cats that you have observed purr. Therefore, every cat must
•All students that have been taught by Mrs. Smith are right handed.
So, Mrs. Smith assumes that all students are right handed.
17. •John is a financial analyst. Individuals with
professions in finance are very serious people. John
is a very serious person.
•Jerry is a bartender. Bartenders are friendly. Jerry is
assumed to be friendly.
•All observed brown dogs are small dogs. Therefore,
all small dogs are brown.
•All observed children like to play with Legos. All
children, therefore, enjoy playing with Legos.
•The water at the beach has always been about 75
degrees in July. It is July. The water will be about 75
•All observed police officers are under 50 years old.
John is a police officer. John is under 50 years old.
•Mary and Sue are friends. Mary enjoys fishing,
running and rock climbing. Sue likes fishing and rock
climbing. Sue must also like running.
18. •Barry is a baseball player. All baseball players can make it to first base
in at least 4 seconds. Barry can make it to first base in at least 4
•Ray is a football player. All football players weigh more than 170
pounds. Ray weighs more than 170 pounds.
•All observed lacrosse players are tall and thin. George plays lacrosse.
It is assumed that George is tall and thin.
•All little dogs are "yappy." Bill has a small dog. His dog barks
frequently at a high pitched level.
•All observed cats in the area are brown. Tiny is a cat. Tiny is brown.
•All observed houses on the South Street are falling apart. Sherry lives
on South Street. Her house is falling apart.
•Jenny is a dancer. Dancers are thin and tall. Jenny is thin and tall.
•Bob is a sumo wrestler. Sumo wrestlers weigh a lot. Bob weighs a lot.
•All observed basketball players are tall, so all basketball players must
•All observed women in one area wear high heels, so all women must
wear high heels.
•Suzy is a doctor. Doctors are smart. Suzy is assumed to be smart.
19. Deductive Reasoning
• In mathematics, If A = B and B = C, then A = C.
• All apples are fruits, all fruits grow on trees; therefore, all apples grow on
• William is a bachelor, all bachelors are single; hence William is single.
Since all humans are mortal, and I am a human, then I am mortal.
• All dolphins are mammals, all mammals have kidneys; therefore all
dolphins have kidneys.
• Since all squares are rectangles, and all rectangles have four sides, so all
squares have four sides.
• If Dennis misses work and at work there is a party, then Dennis will miss
• All numbers ending in 0 or 5 are divisible by 5. The number 35 ends with a
5, so it is divisible by 5.
• The Earth is a planet, and all planets orbit a sun, therefore the Earth orbits
• To earn a master’s degree, a student must have 32 credits. Tim has 40
credits, so Tim will earn a master’s degree.
• All birds have feathers and robins are birds, so robins have feathers.
20. • It is dangerous to drive on icy streets. The streets are icy now so it is dangerous to
• All cats have a keen sense of smell. Fluffy is a cat, so Fluffy has a keen sense of
• The elm is a tree and all trees have bark, so elms have bark.
• Snakes are reptiles and reptiles are cold-blooded; therefore, snakes are cold-
• Cacti are plants and all plants perform photosynthesis; therefore, cacti perform
• Red meat has iron in it and beef is red meat, so beef has iron in it.
• Acute angles are less than 90 degrees and this angle is 40 degrees so this angle is
• All noble gases are stable and helium is a noble gas, so helium is stable.
• Magnolias are dicots and dicots have two embryonic leaves; therefore magnolias
have two embryonic leaves.
• Elephants have cells in their bodies and all cells have DNA, so elephants have DNA.
• All cars have at least two doors and a Ford Focus is a car, so the Ford Focus has at
least two doors.
• All horses have manes and the Arabian is a horse; therefore Arabians have manes.
21. Deduction Reasoning
• In the process of deduction, you begin with some statements,
called 'premises', that are assumed to be true, you then determine
what else would have to be true if the premises are true. For
example, you can begin by assuming that God exists, and is good,
and then determine what would logically follow from such an
assumption. You can begin by assuming that if you think, then you
must exist, and work from there.
• In mathematics, you can also start will a premise and begin to prove
other equations or other premises. With deduction you can provide
absolute proof of your conclusions, given that your premises are
correct. The premises themselves, however, remain unproven and
unprovable, they must be accepted on face value, or by faith, or for
the purpose of exploration.
• In the process of induction, you begin with some data, and then
determine what general conclusion(s) can logically be derived from
those data. In other words, you determine what theory or theories
could explain the data. For example, you note that the probability
of becoming schizophrenic is greatly increased if at least one parent
is schizophrenic, and from that you conclude that schizophrenia
may be inherited.
• That is certainly a reasonable hypothesis given the data. However,
induction does not prove that the theory is correct. There are often
alternative theories that are also supported by the data. For
example, the behavior of the schizophrenic parent may cause the
child to be schizophrenic, not the genes. What is important in
induction is that the theory does indeed offer a logical explanation
of the data. To conclude that the parents have no effect on the
schizophrenia of the children is not supportable given the data, and
would not be a logical conclusion. 1
• A syllogism is a logical argument composed of
three parts: the major premise, the minor
premise, and the conclusion inferred from the
• Aristotle, from the combination of a general
statement (the major premise) and a specific
statement (the minor premise), a conclusion is
24. • A syllogism is made up of 3 propositions, with
2 being premises and 1 as the conclusion. Of
the two premises, one will be the minor
premise, whereas the other will be a major
• The combination of a general statement (the
major premise) and a specific statement (the
minor premise), a conclusion is deduced.
• All men are mortal (major premise) and that
Socrates is a man (minor premise), we may
validly (conclude) that Socrates is mortal
25. Structure of a Categorical Proposition
• A categorical proposition is a sentence. And
like all sentences, a proposition can be split up
into 4 main grammatical parts: the Quantifier,
Subject Term, the Copula and the Predicate
• (the propositions contain words called
quantifiers, which provide information about
how many members of the class are under
consideration. There are four possible types of
quantifiers. Each of these are given a single-
26. Type of Quantifier English Word Label Example
A All men are mortal
No men are mortal
Some men are mortalISome
Some men are not mortal0
Not all or
Each proposition in a syllogism has the form:
[quantifier] [one term] [is/are] [other term]
27. The Subject term
• The Subject is the "main" in a proposition. It is
the main argument of the whole proposition,
the actor in the sentence. The Subject can be
thought of as the "What we are talking
• Examples include the following: "Socrates" in
"Socrates is mortal" "Throwers" in "All
throwers throw something" "Sparrows" in
"Virtually all sparrows can fly"
28. The Predicate term
• The Predicate tells us something about the
Subject. The Predicate can be thought as the
"What we are talking about of the Subject".
• Examples include the following: "Mortal" in
"Socrates is mortal" "Something" in "All
throwers throw something" "Fly" in "Virtually
all sparrows can fly"
29. The Copula (linking verb)
• Word or set of words that connect the Subject
• Examples include the following: "Is" in
"Socrates is mortal" "Throw" in "All throwers
throw something" "Can" in "Virtually all
sparrows can fly"
30. The Quantifier
• The extend or number of the subject. (E.g. All, some, none)
• Examples include the following: "All" in "All throwers throw
something" "No" in "No fish can fly" "Virtually all" in
"Virtually all sparrows can fly“
• How does it look like together?
Quantifier Subject Copula Predicat
All S is P
31. All forms of Propositions can exist in one of 4 different types.
These 4 types are denoted by the code letters A,E,I,O. These
code letters are derived from the 2 Latin vowels affirmo (I
affirm) and nego (I deny).
• Type A Universal Affirmative All S is P All
birds have wings
• Type E Universal Negative No S is P No
birds have gills
• Type I Particular Affirmative Some S is P
Some birds can fly
• Type O Particular Negative Some S is not
P Some birds cannot fly
32. Type A - Universal Affirmative
• All of the subject will be distributed in the
class defined by the predicate.
• Example: All birds have wings
33. Type E - Universal Negative
• None of the subject will be distributed in the
class defined by the predicate.
• Example: No birds have gills
34. Type I - Paraticular Affirmative
• Some of the subject will be distributed in the
class defined by the predicate.
• Example: Some birds can fly
35. Type O - Particular Negative
Some of the subject will not be distributed in the class defined by the predicate.
Some birds cannot fly