Introduction to logic presentation

1. Logic
BBA/BS & MBA
Logic and Propositions
Module 1B
Course Lecturer: Farhan Mir

4. Logic & Propositions

5. Overview
• What is Logic?
• Propositions

6. What is Logic?
• Logic: the study of the methods and
principles used to distinguish good from
bad reasoning
• Synonyms for reasons: “backing up,”
support, arguments, evidence, justification
– Distinguished from rhetoric and persuasion

7. Propositions
• Proposition: an abstract entity that asserts
something is the case.
– Synonyms: statement, claim
– Is the kind of thing that is either true or false

8. Proposition
• A proposition is a declarative sentence (a
sentence that declares a fact) that is either
true or false, but not both.
• Are the following sentences propositions?
– Toronto is the capital of Canada.
– Read this carefully.
– 1+2=3
– x+1=2
– What time is it?
(No)
(No)
(No)
(Yes)
(Yes)
8

9. Propositions ≠ sentences
• A sentence is a linguistic entity, i.e., it is
made up of sounds or images;
• Declarative sentences express
propositions, which are abstract entities.
– Ex. “It’s raining” and “Il pleut” are two
sentences, but they express the same
proposition, i.e., it’s raining.

10. Hercules is the Strongest man ever
lived on Earth

11. Proposition Example
• Hercules is the Strongest man ever lived on
Earth; He could lift up to 100 tons. If the sky
falls Hercules could be the one to hold it at his
shoulders

12. Testing for proposition-hood
• Take a sentence. Attach
“It’s true that” or “It’s
false that” to it.
• If the resulting sentence
is grammatical, then it’s
a proposition.
• Ex. it’s
raining.
• Ex.
Khalifa is evil.
It’s true that
It’s false that
Both sentences
express
propositions!
But one
might be
misleading!

13. Sentences that do not express
propositions
• Questions
– Ex. What time is it?
• Imperatives
– Ex. Do your homework.
• Exclamations
– Ex. Holy crap!
It’s false that
This doesn’t
make sense!
It’s true that
It’s true that
Holy crap! This
is nonsense
too!

14. How can imperatives be turned into
propositions?
• Do your homework.
– You should do your homework.
– Doing your homework is good.
– Your homework is worth doing.
Can you think of examples
of questions or
exclamations that express
propositions?

15. Compound propositions
• Compound proposition: proposition composed of
other propositions.
• Conjunctions (P and Q)
– Khalifa is smart and Khalifa is handsome.
• Disjunctions (P or Q)
– Either you do your homework or you go to the
concert.
• Conditionals (If P then Q)
– If you do your homework, then you will pass.
• Under what conditions are these statements
false?

16. Recap
• Logic studies the methods and principles
used to distinguish good from bad
reasoning
• Propositions are the basic building blocks
of reasoning
• Propositions are the kinds of things that
can be true or false, and reasoning aims
to ascertain what is true and what is
false.

17. Propositions in Business
• The proposition is an easy-to-understand
reason why a customer should buy a
product or service from that particular
business. A value proposition should
clearly explain how a product fills a need,
communicate the specifics of its added
benefit, and state the reason why it's
better than similar products on the market.

18. Propositions example: Choose Us
because

19. Propositions example: Choose Us
because