Presocratics

Theories of Perception

  1. Top Down—background beliefs afffect how things look
  2. Bottom Up—background beliefs do not affect perception

Assumptions and Methodology of Presocratics

  1. Assumption of Plurality: lots of different things
  2. Assumption of Motion: things move and change
  3. Reductionism: there are less different kinds of things than it might seem. It makes “science” easier. You just learn the laws of the few kinds and then you can explain everything else. Note: reductionism is not a denial of the assumption of plurality. One could be a pluralist reductionist—there are lots of different things, but they’re all made out of the same stuff.

The Presocratic Philosophers

Philosophers in ancient Greece dating from 600–470 B.C.E.

Thales

600 BCE Everything is water. Isn’t it obvious that not everything water?? Appearances are misleading. Things aren’t always as they seem. Sometimes you have to trust reason over perception. Thales says to trust reason over perception when perception tells you something is not water. Accept assumption of plurality. Accepts assumption of motion.

Pythagoreans

560 BCE. A group of “philsophers” founded by Pythagoras. They thought mathematics was really neat. Numbers are what everything is at bottom. Everything is numbers. Reductionists. Accept assumption of the plurality. It’s not clear whether they accept the assumption of motion. Never trust perception; Only reason (mathematical reasoning). They proved the pythagorean theorem. They also “discovered” irrational numbers. THese are numbers that can’t be represented by a fraction (like pi).

Heraclitus

540 BCE

“You can’t step into the same river twice.” Point is: everything is constantly changing.

Q: How can you know anything if everything is always changing?

A: The Logos.

The Logos is something like the laws of nature. Laws of nature don’t change, but they do explain how everything else changes. So all have you to do is learn about the Logos, and you’ll be able to understand the world.

Is he a reductionist? It’s not clear. He does accept the assumption of motion. And he seems to accept the assumption of pluarility.

Democritus

460 BCE

He’s an “atomist.” Everything is made out of atoms. What are atoms?

They explain how things change:

Two other things: the Void, empty space before anything existed. Then the Swerve occurred. (something like the big bang). The initial event that got the atoms moving.

Parmenides

500 BCE

Denies assumption of plurality and the assumption of motion. There’s only one thing and it never changes.

This is called “Monism”—one-thing-ism. The One doesn’t have parts. You can’t understand it or even really think about it.

Why think this? Parmenides has an argument.

Sidenote: An argument is a set of reasons for thinking something is true.

  1. All men are mortal.
  2. Parmenides was a man.
  3. Conclusion: Parmenides was mortal.

End sidenote. Back to Parmenides and his argument for the impossibility of change.

  1. If change were possible, then something could come from nothing. (x turns into a butterfly only if it was once not a butterfly. But not-butterflies aren’t anything—they’re nothings. So if x turned into a butterfly, then x was once nothing)
  2. Something can’t come from nothing.
  3. Conclusion: Change is not possible.

Now why think there’s only one thing? Argument:

  1. If there’s more than one thing, then there are at least two things, x and y, such that x does not equal y.
  2. So x is equal to not-y.
    3. But not-y is nothing—it doesn’t exist.
  4. So x is nothing—x doesn’t exist
  5. That contradicts our assumption in (1) that x exists.
    6. Conclusion: So there’s only one thing. (Monism is true)

Zeno

(Dates?)

Zeno denies pluarlity and motion. Let’s look at his argument that there is no motion.