Notes for 10/26/2026

  

10/20/2026

 

 [Philosophy Club every Wednesday, 5-6 pm, in the Buchtel College of Arts and Sciences room 436 ("The Cave")

Bioethics Club Tuesdays from 4:30-5:30 in CAS 436.]

 

How might you go about proving that something is the same rather than merely similar?

 

Where do the ideas of similarity and sameness come from?

 

Similarity seems for Locke to be a primitive function of the mind (idea of reflection, but that idea of similarity seems to presuppose objective similarity in the objects it considers)

 

Sameness, for Locke is also an idea of reflection where the mind “counts the same idea twice” (this very idea is this very idea).

 

 

When do we know that we are applying the idea of sameness vs similarity to the objects of perception?

 

 

The idea of sameness is limited initially to single acts of perception. (This very thing I am perceiving at this moment.)

Sameness is initially always synchronic (at one particular time).

x at time t is identical to y at time t if and only if the idea of x at t is the very same idea as the idea of y at t.

 

For Locke, this requires thinking of a thing as occupying a particular place (spatial location) at a particular time.

 

That is, the primary idea of identity (x=x) for material things reduces to the idea of occupying a particular place at a particular time.

The basic idea of material difference, then, reduces to occupying different places at the same time. (Material co-location is excluded as meaningful because this could never be grounded in experience.)

 

Diachronic identity = identity across times (at different times)

 

Occupying a unique spatial and temporal location is the basis of the idea of synchronic material identity.

 

What is the basis of the idea of diachronic identity of objects of experience?

Diachronic identity seems to violate Leibniz’s Law.

(Locke disagrees with Leibniz’s view that spatial & temporal differences presuppose intrinsic differences.)

 

 

 

For Locke, the answer is “continuity”. If I look at something for 10 seconds, this gives me the idea of diachronic identity.

 

This is true whether what I look at is stationary or moves.

 

(What would Locke say about teleportation?)

 

 

 

A thing’s existence begins at a particular place and a particular time.

 

So for atoms, each atom is identical with itself in virtue of having a particular origin in space and time.

 

Composite things possess diachronic identity insofar as their component parts possess diachronic identity.

 

 

 

But what happens when a composite thing’s parts change?

 

We apply the concept of identity in some of these cases. How? Why?

 

 

Diachronic identity with change

 

 

 

Ship of Theseus

Ship of Perseus

 

 

 

 

 

Is the ship the same over time, and if so, what MAKES it the same ship over time.

 

Why do we THINK of the ship as the same over time?

 

 

 

Why do we apply the idea of identity in some cases and the idea of mere similarity in others? In the latter case, it is because we think there must be other differences of the things (especially spatial & temporal properties).

 

 

But consider:

Suppose you left a hat in this room last week. What would lead you to think a hat you find here today is the same hat rather than an exactly similar one? What could convince you that it was similar rather than the same?

 

 

 

 

 

Empiricist criterion of meaning: If two ideas are meaningfully different, then there must be some in-principle experiential difference in the application of those ideas.

 

Diachronic identity judgments are problematic because we apply the concept of identity in lots of cases where the things identified are NOT perfectly similar.

 

We find these especially in:

-     Artifacts (such as ships)

-     Vegetables (plants)

-     Animals

-     (collections of material parts)

-     (Souls)

-     Persons