1. Introduction to Philosophy
Lecture 2:
Plato
Logic and Arguments

2. Quiz
A(n) ___________ argument is an argument which Is valid and which contains only true premises.
A(n) ___________ argument is invalid if and only if it is necessary that if all the premises are true, then the conclusion is true.
A(n) ___________ argument is a sound argument that is recognized to be such in virtue of the presentation of its structure.
Cogent
Sound
Valid
Identify the three metaphors from Plato that the authored discussed.

3. Plato

4. Three Metaphors
The Sun
The Divided Line
The Cave

5. The Sun

6. The Argument I see something; how is this possible? We need:
Some faculty that allows vision (eye and brain)
An external object to see
A source (light) that creates the conditions of vision
This applies more or less to concepts and higher realities.
For us to think about a square (a concept) we require:
A faculty (soul)
An external object (the concept of squareness)
Something that grounds this thought (the Idea or Form of a square)
The physical Sun is the grounds of observable reality
The Good is the grounds of all incorporeal reality

7. The Divided Line Knowledge Understanding Belief Contemplative Reason
Shadows/Phantasms
The Forms
Physical Objects
Concepts

8. The Argument Follows from the discussion of the Sun metaphor…
Some things we see are illusions and are the domain of opinion.
Some things we see are accessible by all and considered real (in the sense of physical location), these are in the domain of belief.
Some things we gain access to through critical thinking and logic (e.g., concepts, definitions, etc.) and these are the domain of logical analysis.
Some things are only accessible by moving beyond the base matter or definition of something and perceiving its Form. These are in the domain of contemplative reason.

9. The Cave

10. The Journey We begin as people who see shadows of real things.
We move to looking at the things casting the shadows.
We move higher by looking for definitions and concepts of the objects we perceive.
We exit the cave by looking for the abstract truth behind concepts.
This is a progression from little or no truth/reality to the fullest and highest truth/reality.
We perceive by virtue of our innate faculties (organs, souls) and the source of our perceptions (light, the Good)
Moving from the lower stages to the higher stages…
Is painful and uncomfortable
Requires a guide and coach
Gives deeper and richer clarity as one progresses

11. Bad Plato
Plato’s political philosophy is often criticized because of his rather prejudiced perception of human ability in general.
He proposed that people are born with a certain capacity for advancing out of the cave.
A person would accept his/her social role according to whatever capacity they had for Reality.
This leads to a deep-seated elitism and the invention of a “philosopher king” who rules authoritatively over the “lesser” humans.

12. Good Plato Deeply influential on primitive Christianity
"The safest general characterization of the European philosophical tradition is that it consists of a series of footnotes to Plato” (A. N. Whitehead)
The Matrix is more or less the allegory of the cave reworked for a modern technological era.
Mumford and Sons – “the Cave”

13. Arguments
An argument is a sequence of two or more propositions of which one is designated as the conclusion and all the others of which are premises.
Proposition: a statement that expresses an opinion
Premise: a statement (proposition) from which a conclusion is drawn
Example
All humans are mortals.
Socrates is a human.
_____________________
Therefore, Socrates is mortal.
Premise 1
Premise 2
Conclusion

14. Valid Arguments
An argument is valid if and only if it is necessary that if all the premises are true, then the conclusion is true.
In English: For an argument to be valid its conclusion must follow from its premises.
Examples I am an astronaut All astronauts have blonde hair I have blonde hair Notice that the premises can be true or false, but so long as the premises entail the conclusion it is a valid argument.
Entail: to involve something as a necessary or inevitable part or consequence.

15. Sound Arguments
A sound argument is an argument which is valid and contains only true premises.
Its conclusion must follow from its premises
The premises must be proved to be true themselves.
Consider the argument: All humans are mortal. Socrates is a human Socrates is mortal For this argument to be sound it must be proven an accepted that (1) all humans are mortal and (2) that Socrates is a human.
Because people disagree on what is true and untrue almost as a fact of human nature, a universally recognized sound argument is rare to come by.

16. Cogent Arguments
A cogent argument is a sound argument that is recognized to be such in virtue of the presentation of its structure and content.
The cogency of an argument depends on (1) the audience it is presented to and (2) the form the argument is presented in.
Consider a sermon:
A sermon can be considered an argument of sorts, they are intended to be persuasive, but sermons are rarely constructed as a set of premises and a conclusion.
Someone who is un-churched might not be convinced by a sermon because they are not used to receiving new information this way. Therefore a sermon is not a cogent argument to this person, but it is (usually) cogent to the congregation.
It is possible to distill most sermons into the form of a logical argument. If we did that, it is likely that un-churched people might recognize it as cogent (so long as they also agree it is sound).
So it all depends on who your audience is and how you say it.