Logic comes from the word
“LOGOS”, which means “REASON”.
It is concerned with the methods and
rules for correct thinking.
LOGIC: The SCIENCE and ART
•Logic, as an ART, on one hand, direct
reason. As an ART it guides man’s reason
so that he can proceed with order and
precision in the search for meaning.
•Logic as a SCIENCE, on the other
hand, “investigates, discovers,
demonstrates, and explains the laws
of correct thinking.
METHODS OF REASONING
1.INDUCTIVE METHOD – where we can
obtain universal knowledge by considering
the particular things.
2.DEDUCTIVE KNOWLEDGE – when we
proceed from universal knowledge to
DIVISION OF LOGIC
1. Material Logic – this focuses on the study of
the main philosophical problems taken up in
logic such as problems of the universals,
abstraction, or inductions.
2. Formal Logic – this is centered on the
operation of the mind from the point of view
of correct thinking.
Material Logic : Acts/Level of the Mind
• Simple Apprehension
It is the basic operation of the mind or
“the mental process by which we grasp the
general meaning of the thing without
affirming or denying anything about it”.
It is the act of the mind by which we
compare two, concepts, either they agree
or not. If we put concepts together, the
end result is called judgment or
Is the act of mind by which we derive
new truths from previously assumed truth.
The mind combines several judgments or
propositions in order to arrive at a previously
unknown judgment, it is called syllogism.
Levels of Expressions
A term is a word that denotes a
particular object. By denoting a term
brings us an object or idea.
Types of TERM
• Simple and Complex
• Significant and Non-Significant
• Distributive and Collective
• Univocal, Equivocal and Analogical
• Contrary and Contradictory
Simple and Complex
• Simple – when the term used consists of a
word, for instance “Jesus” such is called a
• Complex – composed of many term but
standing one idea. Example, The lady in red
walking down the street.
Significant and Non-Significant
• Significant – when a term is used to
directly express a concept, it is called a
•Non-Significant – when it is not points
directly to the nature of a thing.
Distributive and Collective
• Distributive – a term is distributive when
it shows the essence of entities singularity.
• Collective – a term is collective when it
shows the essence of entities as a group.
Univocal, Equivocal and Analogical
• Univocal – a term is said to be
univocal when it has the same
• Equivocal – a term is said to
be equivocal when it is used in
entirely different sense.
• Analogical – a term is said to
be analogical when it is used in
distinct but related senses.
Contrary and Contradictory
• Contrary – terms are ones that
represent two extremes of the
• Contradictory – terms are ones
that are totally opposed to each
A Proposition is a sentence in which
the subject and predicate are combined in
order to state something as true or false. A
Proposition therefore either affirms or
The valid Propositional sentence excludes the
Exclamatory, Interrogative, and the Imperative.
• Exclamatory Sentence – express
emotions. Example: Give me liberty
or give me death!
• Interrogative Sentence – ask
questions. Example: Am I my
• Imperative Sentence – give orders.
Example: Send this Order to the
Parts of the Propositions
• Subject – is a bout which something is
affirmed or denied.
• Predicate – is what affirmed or denied to
• Copula – is either is (am, are) if
affirmative or is not (am not, are not) if
Types of the Proposition
Nouns modified by adjective in
Singular (5 signs)
Particular (4 signs)
Article “A” and “AN”
Use of numbers
Universality (3 signs)
Article a, an, and the
Classification of Proposition
Particular I O
The symbols A, E, I, O indicate the
classification of categorical proposition on
the basis of quantity and quality.
Inference is a process by which
the mind draws new knowledge or
insight from any given proposition or a
set of proposition. Inference must follow
the valid sequence of premises.
Types of Inference
Immediate Inference – when there is no
intermediary in deriving an opposite insight.
Mediate Inference – for instance the
categorical syllogism, when there is an
intermediary, i.e. . Middle term.