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All the ideas for 'Philosophy of Mathematics', 'Axiomatic Theories of Truth (2013 ver)' and 'Action, Reasons and Causes'

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23 ideas

2. Reason / D. Definition / 8. Impredicative Definition
Predicative definitions only refer to entities outside the defined collection [Horsten]
     Full Idea: Definitions are called 'predicative', and are considered sound, if they only refer to entities which exist independently from the defined collection.
     From: Leon Horsten (Philosophy of Mathematics [2007], §2.4)
3. Truth / A. Truth Problems / 2. Defining Truth
If we define truth, we can eliminate it [Halbach/Leigh]
     Full Idea: If truth can be explicitly defined, it can be eliminated.
     From: Halbach,V/Leigh,G.E. (Axiomatic Theories of Truth (2013 ver) [2013], 1.3)
     A reaction: That we could just say p corresponds to the facts, or p coheres with our accepted beliefs, or p is the aim of our enquiries, and never mention the word 'true'. Definition is a strategy for reduction or elimination.
3. Truth / F. Semantic Truth / 1. Tarski's Truth / b. Satisfaction and truth
If a language cannot name all objects, then satisfaction must be used, instead of unary truth [Halbach/Leigh]
     Full Idea: If axioms are formulated for a language (such as set theory) that lacks names for all objects, then they require the use of a satisfaction relation rather than a unary truth predicate.
     From: Halbach,V/Leigh,G.E. (Axiomatic Theories of Truth (2013 ver) [2013], 3.3)
     A reaction: I take it this is an important idea for understanding why Tarski developed his account of truth based on satisfaction.
3. Truth / F. Semantic Truth / 1. Tarski's Truth / c. Meta-language for truth
Semantic theories need a powerful metalanguage, typically including set theory [Halbach/Leigh]
     Full Idea: Semantic approaches to truth usually necessitate the use of a metalanguage that is more powerful than the object-language for which it provides a semantics. It is usually taken to include set theory.
     From: Halbach,V/Leigh,G.E. (Axiomatic Theories of Truth (2013 ver) [2013], 1)
     A reaction: This is a motivation for developing an axiomatic account of truth, that moves it into the object language.
3. Truth / F. Semantic Truth / 2. Semantic Truth
The T-sentences are deductively weak, and also not deductively conservative [Halbach/Leigh]
     Full Idea: Although the theory is materially adequate, Tarski thought that the T-sentences are deductively too weak. …Also it seems that the T-sentences are not conservative, because they prove in PA that 0=0 and ¬0=0 are different, so at least two objects exist.
     From: Halbach,V/Leigh,G.E. (Axiomatic Theories of Truth (2013 ver) [2013], 3.2)
     A reaction: They are weak because they can't prove completeness. This idea give two reasons for looking for a better theory of truth.
3. Truth / G. Axiomatic Truth / 1. Axiomatic Truth
A natural theory of truth plays the role of reflection principles, establishing arithmetic's soundness [Halbach/Leigh]
     Full Idea: If a natural theory of truth is added to Peano Arithmetic, it is not necessary to add explicity global reflection principles to assert soundness, as the truth theory proves them. Truth theories thus prove soundess, and allows its expression.
     From: Halbach,V/Leigh,G.E. (Axiomatic Theories of Truth (2013 ver) [2013], 1.2)
     A reaction: This seems like a big attraction of axiomatic theories of truth for students of metamathematics.
If deflationary truth is not explanatory, truth axioms should be 'conservative', proving nothing new [Halbach/Leigh]
     Full Idea: If truth does not have any explanatory force, as some deflationists claim, the axioms of truth should not allow us to prove any new theorems that do not involve the truth predicate. That is, a deflationary axiomatisation of truth should be 'conservative'.
     From: Halbach,V/Leigh,G.E. (Axiomatic Theories of Truth (2013 ver) [2013], 1.3)
     A reaction: So does truth have 'explanatory force'? These guys are interested in explaining theorems of arithmetic, but I'm more interested in real life. People do daft things because they have daft beliefs. Logic should be neutral, but truth has values?
3. Truth / G. Axiomatic Truth / 2. FS Truth Axioms
The FS axioms use classical logical, but are not fully consistent [Halbach/Leigh]
     Full Idea: It is a virtue of the Friedman-Sheard axiomatisation that it is thoroughly classical in its logic. Its drawback is that it is ω-inconsistent. That is, it proves &exists;x¬φ(x), but proves also φ(0), φ(1), φ(2), …
     From: Halbach,V/Leigh,G.E. (Axiomatic Theories of Truth (2013 ver) [2013], 4.3)
     A reaction: It seems the theory is complete (and presumably sound), yet not fully consistent. FS also proves the finite levels of Tarski's hierarchy, but not the transfinite levels.
3. Truth / G. Axiomatic Truth / 3. KF Truth Axioms
KF is formulated in classical logic, but describes non-classical truth, which allows truth-value gluts [Halbach/Leigh]
     Full Idea: KF is formulated in classical logic, but describes a non-classical notion of truth. It allow truth-value gluts, making some sentences (such as the Liar) both true and not-true. Some authors add an axiom ruling out such gluts.
     From: Halbach,V/Leigh,G.E. (Axiomatic Theories of Truth (2013 ver) [2013], 4.4)
     A reaction: [summary, which I hope is correct! Stanford is not wholly clear]
5. Theory of Logic / J. Model Theory in Logic / 2. Isomorphisms
A theory is 'categorical' if it has just one model up to isomorphism [Horsten]
     Full Idea: If a theory has, up to isomorphism, exactly one model, then it is said to be 'categorical'.
     From: Leon Horsten (Philosophy of Mathematics [2007], §5.2)
6. Mathematics / B. Foundations for Mathematics / 2. Proof in Mathematics
Computer proofs don't provide explanations [Horsten]
     Full Idea: Mathematicians are uncomfortable with computerised proofs because a 'good' proof should do more than convince us that a certain statement is true. It should also explain why the statement in question holds.
     From: Leon Horsten (Philosophy of Mathematics [2007], §5.3)
6. Mathematics / B. Foundations for Mathematics / 6. Mathematics as Set Theory / a. Mathematics is set theory
The concept of 'ordinal number' is set-theoretic, not arithmetical [Horsten]
     Full Idea: The notion of an ordinal number is a set-theoretic, and hence non-arithmetical, concept.
     From: Leon Horsten (Philosophy of Mathematics [2007], §2.3)
7. Existence / B. Change in Existence / 4. Events / b. Events as primitive
Varied descriptions of an event will explain varied behaviour relating to it [Davidson, by Macdonald,C]
     Full Idea: Davidson points out that we can only make sense of patterns of behaviour such as excuses if events can have more than one description. So I flip the light switch, turn on the light, illuminate the room, and alert a prowler, but I do only one thing.
     From: report of Donald Davidson (Action, Reasons and Causes [1963]) by Cynthia Macdonald - Varieties of Things Ch.5
     A reaction: We can distinguish an event as an actual object, and as an intentional object. We can probably individuate intentional events quite well (according to our interests), but actual 'events' seem to flow into one another and overlap.
8. Modes of Existence / B. Properties / 12. Denial of Properties
We can reduce properties to true formulas [Halbach/Leigh]
     Full Idea: One might say that 'x is a poor philosopher' is true of Tom instead of saying that Tom has the property of being a poor philosopher. We quantify over formulas instead of over definable properties, and thus reduce properties to truth.
     From: Halbach,V/Leigh,G.E. (Axiomatic Theories of Truth (2013 ver) [2013], 1.1)
     A reaction: [compressed] This stuff is difficult (because the axioms are complex and hard to compare), but I am excited (yes!) about this idea. Their point is that you need a truth predicate within the object language for this, which disquotational truth forbids.
8. Modes of Existence / E. Nominalism / 1. Nominalism / c. Nominalism about abstracta
Nominalists can reduce theories of properties or sets to harmless axiomatic truth theories [Halbach/Leigh]
     Full Idea: The reduction of second-order theories (of properties or sets) to axiomatic theories of truth is a form of reductive nominalism, replacing existence assumptions (e.g. comprehension axioms) by innocuous assumptions about the truth predicate.
     From: Halbach,V/Leigh,G.E. (Axiomatic Theories of Truth (2013 ver) [2013], 1.1)
     A reaction: I'm currently thinking that axiomatic theories of truth are the most exciting development in contemporary philosophy. See Halbach and Horsten.
20. Action / A. Definition of Action / 2. Duration of an Action
If one action leads directly to another, they are all one action [Davidson, by Wilson/Schpall]
     Full Idea: Davidson (1980 ess 1) agreed with Anscombe that if a person Fs by G-ing, then her act F = her act G. For example, if someone accidentally alerts a burglar, by deliberately turning on a light, by flipping a switch, these are all the same action.
     From: report of Donald Davidson (Action, Reasons and Causes [1963]) by Wilson,G/Schpall,S - Action 1.2
     A reaction: I would have thought there was obviously a strong conventional element in individuating actions, depending on interest. An electrician is only interest in whether the light worked. The police are only interested in the disturbance of the burglar.
20. Action / B. Preliminaries of Action / 1. Intention to Act / a. Nature of intentions
We explain an intention by giving an account of acting with an intention [Davidson, by Stout,R]
     Full Idea: The early Davidson championed the approach that we explain the idea of having an intention by providing an account of what it is to act with an intention.
     From: report of Donald Davidson (Action, Reasons and Causes [1963]) by Rowland Stout - Action 7 'Conclusion'
     A reaction: This eliminates the distinction between a prior intention, and the intention that maintains a process such as speech. It sounds almost behaviourist.
20. Action / C. Motives for Action / 2. Acting on Beliefs / a. Acting on beliefs
Acting for a reason is a combination of a pro attitude, and a belief that the action is appropriate [Davidson]
     Full Idea: Whenever someone does something for a reason he can be characterised as (a) having some sort of pro attitude towards action of a certain kind, and (b) believing (or knowing, perceiving, noticing, remembering) that his action is of that kind.
     From: Donald Davidson (Action, Reasons and Causes [1963], p.3-4), quoted by Rowland Stout - Action 3 'The belief-'
     A reaction: This is the earlier Davidson roughly endorsing the traditional belief-desire account of action. He is giving a reductive account of reasons. Deciding reasons were not reducible may have led him to property dualism.
20. Action / C. Motives for Action / 3. Acting on Reason / c. Reasons as causes
The best explanation of reasons as purposes for actions is that they are causal [Davidson, by Smith,M]
     Full Idea: Davidson argues that the best interpretation of the teleological character of reason explanations is an intepretation in causal terms.
     From: report of Donald Davidson (Action, Reasons and Causes [1963]) by Michael Smith - The Moral Problem 4.4
     A reaction: That is, this is the explanation of someone doing something 'because' they have this reason (rather than happening to have a reason). Smith observes that other mental states (such as beliefs) may also have this causal power.
Reasons can give purposes to actions, without actually causing them [Smith,M on Davidson]
     Full Idea: Only the Humean theory is able to make sense of reason explanation as a species of teleological explanation, and one may accept that reason explanations are teleological without accepting that they are causal.
     From: comment on Donald Davidson (Action, Reasons and Causes [1963]) by Michael Smith - The Moral Problem 4.6
     A reaction: That is, reasons can give a purpose to an action, and thereby motivate it, without actually causing it. I agree with Smith. I certainly don't (usually, at least) experience reasons as directly producing my actions. Hume says desires are needed.
Early Davidson says intentional action is caused by reasons [Davidson, by Stout,R]
     Full Idea: In Davidson's earlier approach, intentional action requires causation by reasons.
     From: report of Donald Davidson (Action, Reasons and Causes [1963]) by Rowland Stout - Action 8 'Weakness'
     A reaction: A very Kantian idea, and one that seems to bestow causal powers on something which I take to be highly abstract. Thus Davidson was wrong (but in a nice way).
Reasons must be causes when agents act 'for' reasons [Davidson, by Lowe]
     Full Idea: It can be argued (by Davidson) that far from it being the case that reasons for and causes of action are quite distinct, reasons must be causes when agents act 'for' reasons.
     From: report of Donald Davidson (Action, Reasons and Causes [1963]) by E.J. Lowe - Introduction to the Philosophy of Mind Ch.9
     A reaction: Lowe argues against this view. The rival views to Davidson would be either that reasons are no more than desires-plus-beliefs in disguise, or that the will causes actions, and strong reasons carry a great weight with the will. I like the will.
Davidson claims that what causes an action is the reason for doing it [Davidson, by Kim]
     Full Idea: Davidson defends the simple thesis that the reason for which an action is done is the one that causes it, …which means that agency is possible only if mental causation is possible.
     From: report of Donald Davidson (Action, Reasons and Causes [1963]) by Jaegwon Kim - Philosophy of Mind p.127