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Single Idea 19295
[filed under theme 6. Mathematics / C. Sources of Mathematics / 6. Logicism / c. Neo-logicism
]
Full Idea
The existence of the natural numbers is not a matter of pure logic - it cannot be proved in pure logic. It can be proved in second-order logic plus Hume's principle. Truths of arithmetic are not logic - they depend on the nature of natural numbers.
Gist of Idea
Add Hume's principle to logic, to get numbers; arithmetic truths rest on the nature of the numbers
Source
Bob Hale (Necessary Beings [2013], 07.4)
Book Ref
Hale,Bob: 'Necessary Beings' [OUP 2013], p.177
A Reaction
Hume's principles needs entities which can be matched to one another, so a certain ontology is needed to get neo-logicism off the ground.
The
23 ideas
from 'Necessary Beings'
19275
|
You cannot understand what exists without understanding possibility and necessity
[Hale]
|
19276
|
The big challenge for essentialist views of modality is things having necessary existence
[Hale]
|
19278
|
There is no gap between a fact that p, and it is true that p; so we only have the truth-condtions for p
[Hale]
|
19279
|
What are these worlds, that being true in all of them makes something necessary?
[Hale]
|
19281
|
Interesting supervenience must characterise the base quite differently from what supervenes on it
[Hale]
|
19282
|
It seems that we cannot show that modal facts depend on non-modal facts
[Hale]
|
19286
|
'Absolute necessity' is when there is no restriction on the things which necessitate p
[Hale]
|
19285
|
Logical necessity is something which is true, no matter what else is the case
[Hale]
|
19287
|
Maybe each type of logic has its own necessity, gradually becoming broader
[Hale]
|
19288
|
Logical and metaphysical necessities differ in their vocabulary, and their underlying entities
[Hale]
|
19289
|
Maybe conventionalism applies to meaning, but not to the truth of propositions expressed
[Hale]
|
19290
|
Absolute necessities are necessarily necessary
[Hale]
|
19291
|
A canonical defintion specifies the type of thing, and what distinguish this specimen
[Hale]
|
19293
|
Essentialism doesn't explain necessity reductively; it explains all necessities in terms of a few basic natures
[Hale]
|
19294
|
If necessity derives from essences, how do we explain the necessary existence of essences?
[Hale]
|
19295
|
Add Hume's principle to logic, to get numbers; arithmetic truths rest on the nature of the numbers
[Hale]
|
19296
|
If second-order variables range over sets, those are just objects; properties and relations aren't sets
[Hale]
|
19297
|
The two Barcan principles are easily proved in fairly basic modal logic
[Hale]
|
19298
|
Unlike axiom proofs, natural deduction proofs needn't focus on logical truths and theorems
[Hale]
|
19299
|
Possible worlds make every proposition true or false, which endorses classical logic
[Hale]
|
19300
|
The molecules may explain the water, but they are not what 'water' means
[Hale]
|
19301
|
With a negative free logic, we can dispense with the Barcan formulae
[Hale]
|
19302
|
If a chair could be made of slightly different material, that could lead to big changes
[Hale]
|