Combining Philosophers

All the ideas for Moses Schönfinkel, Christopher Peacocke and E.J. Lemmon

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74 ideas

2. Reason / D. Definition / 13. Against Definition

12585	Most people can't even define a chair [Peacocke]
	Full Idea: Ordinary speakers are notoriously unsuccessful if asked to offer an explicit definition of the concept 'chair'.
	From: Christopher Peacocke (A Study of Concepts [1992], 6.1)

4. Formal Logic / B. Propositional Logic PL / 1. Propositional Logic

9535	'Contradictory' propositions always differ in truth-value [Lemmon]
	Full Idea: Two propositions are 'contradictory' if they are never both true and never both false either, which means that ¬(A↔B) is a tautology.
	From: E.J. Lemmon (Beginning Logic [1965], 2.3)

4. Formal Logic / B. Propositional Logic PL / 2. Tools of Propositional Logic / a. Symbols of PL

9514	If A and B are 'interderivable' from one another we may write A -||- B [Lemmon]
	Full Idea: If we say that A and B are 'interderivable' from one another (that is, A |- B and B |- A), then we may write A -||- B.
	From: E.J. Lemmon (Beginning Logic [1965], 1.5)

9513	We write 'P if and only if Q' as P↔Q; it is also P iff Q, or (P→Q)∧(Q→P) [Lemmon]
	Full Idea: We write 'P if and only if Q' as P↔Q. It is called the 'biconditional', often abbreviate in writing as 'iff'. It also says that P is both sufficient and necessary for Q, and may be written out in full as (P→Q)∧(Q→P).
	From: E.J. Lemmon (Beginning Logic [1965], 1.4)
	A reaction: If this symbol is found in a sequence, the first move in a proof is to expand it to the full version.

9512	We write the 'negation' of P (not-P) as ¬ [Lemmon]
	Full Idea: We write 'not-P' as ¬P. This is called the 'negation' of P. The 'double negation' of P (not not-P) would be written as ¬¬P.
	From: E.J. Lemmon (Beginning Logic [1965], 1.2)
	A reaction: Lemmons use of -P is no longer in use for 'not'. A tilde sign (squiggle) is also used for 'not', but some interpreters give that a subtly different meaning (involving vagueness). The sign ¬ is sometimes called 'hook' or 'corner'.

9511	We write the conditional 'if P (antecedent) then Q (consequent)' as P→Q [Lemmon]
	Full Idea: We write 'if P then Q' as P→Q. This is called a 'conditional', with P as its 'antecedent', and Q as its 'consequent'.
	From: E.J. Lemmon (Beginning Logic [1965], 1.2)
	A reaction: P→Q can also be written as ¬P∨Q.

9508	The sign |- may be read as 'therefore' [Lemmon]
	Full Idea: I introduce the sign |- to mean 'we may validly conclude'. To call it the 'assertion sign' is misleading. It may conveniently be read as 'therefore'.
	From: E.J. Lemmon (Beginning Logic [1965], 1.2)
	A reaction: [Actually no gap between the vertical and horizontal strokes of the sign] As well as meaning 'assertion', it may also mean 'it is a theorem that' (with no proof shown).

9509	That proposition that both P and Q is their 'conjunction', written P∧Q [Lemmon]
	Full Idea: If P and Q are any two propositions, the proposition that both P and Q is called the 'conjunction' of P and Q, and is written P∧Q.
	From: E.J. Lemmon (Beginning Logic [1965], 1.3)
	A reaction: [I use the more fashionable inverted-v '∧', rather than Lemmon's '&', which no longer seems to be used] P∧Q can also be defined as ¬(¬P∨¬Q)

9510	That proposition that either P or Q is their 'disjunction', written P∨Q [Lemmon]
	Full Idea: If P and Q are any two propositions, the proposition that either P or Q is called the 'disjunction' of P and Q, and is written P∨Q.
	From: E.J. Lemmon (Beginning Logic [1965], 1.3)
	A reaction: This is inclusive-or (meaning 'P, or Q, or both'), and not exlusive-or (Boolean XOR), which means 'P, or Q, but not both'. The ∨ sign is sometimes called 'vel' (Latin).

4. Formal Logic / B. Propositional Logic PL / 2. Tools of Propositional Logic / b. Terminology of PL

9516	A 'well-formed formula' follows the rules for variables, ¬, →, ∧, ∨, and ↔ [Lemmon]
	Full Idea: A 'well-formed formula' of the propositional calculus is a sequence of symbols which follows the rules for variables, ¬, →, ∧, ∨, and ↔.
	From: E.J. Lemmon (Beginning Logic [1965], 2.1)

9517	The 'scope' of a connective is the connective, the linked formulae, and the brackets [Lemmon]
	Full Idea: The 'scope' of a connective in a certain formula is the formulae linked by the connective, together with the connective itself and the (theoretically) encircling brackets
	From: E.J. Lemmon (Beginning Logic [1965], 2.1)

9518	A 'theorem' is the conclusion of a provable sequent with zero assumptions [Lemmon]
	Full Idea: A 'theorem' of logic is the conclusion of a provable sequent in which the number of assumptions is zero.
	From: E.J. Lemmon (Beginning Logic [1965], 2.2)
	A reaction: This is what Quine and others call a 'logical truth'.

9529	A wff is 'inconsistent' if all assignments to variables result in the value F [Lemmon]
	Full Idea: If a well-formed formula of propositional calculus takes the value F for all possible assignments of truth-values to its variables, it is said to be 'inconsistent'.
	From: E.J. Lemmon (Beginning Logic [1965], 2.3)

9532	'Subcontrary' propositions are never both false, so that A∨B is a tautology [Lemmon]
	Full Idea: If A and B are expressible in propositional calculus notation, they are 'subcontrary' if they are never both false, which may be tested by the truth-table for A∨B, which is a tautology if they are subcontrary.
	From: E.J. Lemmon (Beginning Logic [1965], 2.3)

9528	A wff is a 'tautology' if all assignments to variables result in the value T [Lemmon]
	Full Idea: If a well-formed formula of propositional calculus takes the value T for all possible assignments of truth-values to its variables, it is said to be a 'tautology'.
	From: E.J. Lemmon (Beginning Logic [1965], 2.3)

9533	A 'implies' B if B is true whenever A is true (so that A→B is tautologous) [Lemmon]
	Full Idea: One proposition A 'implies' a proposition B if whenever A is true B is true (but not necessarily conversely), which is only the case if A→B is tautologous. Hence B 'is implied' by A.
	From: E.J. Lemmon (Beginning Logic [1965], 2.3)

9534	Two propositions are 'equivalent' if they mirror one another's truth-value [Lemmon]
	Full Idea: Two propositions are 'equivalent' if whenever A is true B is true, and whenever B is true A is true, in which case A↔B is a tautology.
	From: E.J. Lemmon (Beginning Logic [1965], 2.3)

9519	A 'substitution-instance' is a wff formed by consistent replacing variables with wffs [Lemmon]
	Full Idea: A 'substitution-instance' is a wff which results by replacing one or more variables throughout with the same wffs (the same wff replacing each variable).
	From: E.J. Lemmon (Beginning Logic [1965], 2.2)

9530	A wff is 'contingent' if produces at least one T and at least one F [Lemmon]
	Full Idea: If a well-formed formula of propositional calculus takes at least one T and at least one F for all the assignments of truth-values to its variables, it is said to be 'contingent'.
	From: E.J. Lemmon (Beginning Logic [1965], 2.3)

9531	'Contrary' propositions are never both true, so that ¬(A∧B) is a tautology [Lemmon]
	Full Idea: If A and B are expressible in propositional calculus notation, they are 'contrary' if they are never both true, which may be tested by the truth-table for ¬(A∧B), which is a tautology if they are contrary.
	From: E.J. Lemmon (Beginning Logic [1965], 2.3)

4. Formal Logic / B. Propositional Logic PL / 2. Tools of Propositional Logic / c. Derivation rules of PL

9393	A: we may assume any proposition at any stage [Lemmon]
	Full Idea: Assumptions (A): any proposition may be introduced at any stage of a proof.
	From: E.J. Lemmon (Beginning Logic [1965], 1.5)

9396	DN: Given A, we may derive ¬¬A [Lemmon]
	Full Idea: Double Negation (DN): Given A, we may derive ¬¬A as a conclusion, and vice versa. The conclusion depends on the assumptions of the premiss.
	From: E.J. Lemmon (Beginning Logic [1965], 1.5)

9399	∧E: Given A∧B, we may derive either A or B separately [Lemmon]
	Full Idea: And-Elimination (∧E): Given A∧B, we may derive either A or B separately. The conclusions will depend on the assumptions of the premiss.
	From: E.J. Lemmon (Beginning Logic [1965], 1.5)

9401	∨E: Derive C from A∨B, if C can be derived both from A and from B [Lemmon]
	Full Idea: Or-Elimination (∨E): Given A∨B, we may derive C if it is proved from A as assumption and from B as assumption. This will also depend on prior assumptions.
	From: E.J. Lemmon (Beginning Logic [1965], 1.5)

9394	MPP: Given A and A→B, we may derive B [Lemmon]
	Full Idea: Modus Ponendo Ponens (MPP): Given A and A→B, we may derive B as a conclusion. B will rest on any assumptions that have been made.
	From: E.J. Lemmon (Beginning Logic [1965], 1.5)

9400	∨I: Given either A or B separately, we may derive A∨B [Lemmon]
	Full Idea: Or-Introduction (∨I): Given either A or B separately, we may derive A∨B as conclusion. This depends on the assumption of the premisses.
	From: E.J. Lemmon (Beginning Logic [1965], 1.5)

9395	MTT: Given ¬B and A→B, we derive ¬A [Lemmon]
	Full Idea: Modus Tollendo Tollens (MTT): Given ¬B and A→B, we derive ¬A as a conclusion. ¬A depends on any assumptions that have been made
	From: E.J. Lemmon (Beginning Logic [1965], 1.5)

9402	RAA: If assuming A will prove B∧¬B, then derive ¬A [Lemmon]
	Full Idea: Reduction ad Absurdum (RAA): Given a proof of B∧¬B from A as assumption, we may derive ¬A as conclusion, depending on the remaining assumptions (if any).
	From: E.J. Lemmon (Beginning Logic [1965], 1.5)

9397	CP: Given a proof of B from A as assumption, we may derive A→B [Lemmon]
	Full Idea: Conditional Proof (CP): Given a proof of B from A as assumption, we may derive A→B as conclusion, on the remaining assumptions (if any).
	From: E.J. Lemmon (Beginning Logic [1965], 1.5)

9398	∧I: Given A and B, we may derive A∧B [Lemmon]
	Full Idea: And-Introduction (&I): Given A and B, we may derive A∧B as conclusion. This depends on their previous assumptions.
	From: E.J. Lemmon (Beginning Logic [1965], 1.5)

4. Formal Logic / B. Propositional Logic PL / 2. Tools of Propositional Logic / d. Basic theorems of PL

9525	We can change conditionals into negated conjunctions with P→Q -||- ¬(P ∧ ¬Q) [Lemmon]
	Full Idea: The proof that P→Q -||- ¬(P ∧ ¬Q) is useful for enabling us to change conditionals into negated conjunctions
	From: E.J. Lemmon (Beginning Logic [1965], 2.2)

9524	We can change conditionals into disjunctions with P→Q -||- ¬P ∨ Q [Lemmon]
	Full Idea: The proof that P→Q -||- ¬P ∨ Q is useful for enabling us to change conditionals into disjunctions.
	From: E.J. Lemmon (Beginning Logic [1965], 2.2)

9527	The Distributive Laws can rearrange a pair of conjunctions or disjunctions [Lemmon]
	Full Idea: The Distributive Laws say that P ∧ (Q∨R) -||- (P∧Q) ∨ (P∧R), and that P ∨ (Q∨R) -||- (P∨Q) ∧ (P∨R)
	From: E.J. Lemmon (Beginning Logic [1965], 2.2)

9522	'Modus ponendo tollens' (MPT) says P, ¬(P ∧ Q) |- ¬Q [Lemmon]
	Full Idea: 'Modus ponendo tollens' (MPT) says that if the negation of a conjunction holds and also one of its conjuncts, then the negation of the other conjunct holds. Thus P, ¬(P ∧ Q) |- ¬Q may be introduced as a theorem.
	From: E.J. Lemmon (Beginning Logic [1965], 2.2)
	A reaction: Unlike Modus Ponens and Modus Tollens, this is a derived rule.

9526	We can change conjunctions into negated conditionals with P→Q -||- ¬(P → ¬Q) [Lemmon]
	Full Idea: The proof that P∧Q -||- ¬(P → ¬Q) is useful for enabling us to change conjunctions into negated conditionals.
	From: E.J. Lemmon (Beginning Logic [1965], 2.2)

9521	'Modus tollendo ponens' (MTP) says ¬P, P ∨ Q |- Q [Lemmon]
	Full Idea: 'Modus tollendo ponens' (MTP) says that if a disjunction holds and also the negation of one of its disjuncts, then the other disjunct holds. Thus ¬P, P ∨ Q |- Q may be introduced as a theorem.
	From: E.J. Lemmon (Beginning Logic [1965], 2.2)
	A reaction: Unlike Modus Ponens and Modus Tollens, this is a derived rule.

9523	De Morgan's Laws make negated conjunctions/disjunctions into non-negated disjunctions/conjunctions [Lemmon]
	Full Idea: The forms of De Morgan's Laws [P∨Q -||- ¬(¬P ∧ ¬Q); ¬(P∨Q) -||- ¬P ∧ ¬Q; ¬(P∧Q) -||- ¬P ∨ ¬Q); P∧Q -||- ¬(¬P∨¬Q)] transform negated conjunctions and disjunctions into non-negated disjunctions and conjunctions respectively.
	From: E.J. Lemmon (Beginning Logic [1965], 2.2)

4. Formal Logic / B. Propositional Logic PL / 3. Truth Tables

9537	Truth-tables are good for showing invalidity [Lemmon]
	Full Idea: The truth-table approach enables us to show the invalidity of argument-patterns, as well as their validity.
	From: E.J. Lemmon (Beginning Logic [1965], 2.4)

9538	A truth-table test is entirely mechanical, but this won't work for more complex logic [Lemmon]
	Full Idea: A truth-table test is entirely mechanical, ..and in propositional logic we can even generate proofs mechanically for tautological sequences, ..but this mechanical approach breaks down with predicate calculus, and proof-discovery is an imaginative process.
	From: E.J. Lemmon (Beginning Logic [1965], 2.5)

4. Formal Logic / B. Propositional Logic PL / 4. Soundness of PL

9536	If any of the nine rules of propositional logic are applied to tautologies, the result is a tautology [Lemmon]
	Full Idea: If any application of the nine derivation rules of propositional logic is made on tautologous sequents, we have demonstrated that the result is always a tautologous sequent. Thus the system is consistent.
	From: E.J. Lemmon (Beginning Logic [1965], 2.4)
	A reaction: The term 'sound' tends to be used now, rather than 'consistent'. See Lemmon for the proofs of each of the nine rules.

4. Formal Logic / B. Propositional Logic PL / 5. Completeness of PL

9539	Propositional logic is complete, since all of its tautologous sequents are derivable [Lemmon]
	Full Idea: A logical system is complete is all expressions of a specified kind are derivable in it. If we specify tautologous sequent-expressions, then propositional logic is complete, because we can show that all tautologous sequents are derivable.
	From: E.J. Lemmon (Beginning Logic [1965], 2.5)
	A reaction: [See Lemmon 2.5 for details of the proofs]

4. Formal Logic / C. Predicate Calculus PC / 2. Tools of Predicate Calculus / a. Symbols of PC

13909	Write '(∀x)(...)' to mean 'take any x: then...', and '(∃x)(...)' to mean 'there is an x such that....' [Lemmon]
	Full Idea: Just as '(∀x)(...)' is to mean 'take any x: then....', so we write '(∃x)(...)' to mean 'there is an x such that....'
	From: E.J. Lemmon (Beginning Logic [1965], 3.1)
	A reaction: [Actually Lemmon gives the universal quantifier symbol as '(x)', but the inverted A ('∀') seems to have replaced it these days]

13902	'Gm' says m has property G, and 'Pmn' says m has relation P to n [Lemmon]
	Full Idea: A predicate letter followed by one name expresses a property ('Gm'), and a predicate-letter followed by two names expresses a relation ('Pmn'). We could write 'Pmno' for a complex relation like betweenness.
	From: E.J. Lemmon (Beginning Logic [1965], 3.1)

13911	The 'symbols' are bracket, connective, term, variable, predicate letter, reverse-E [Lemmon]
	Full Idea: I define a 'symbol' (of the predicate calculus) as either a bracket or a logical connective or a term or an individual variable or a predicate-letter or reverse-E (∃).
	From: E.J. Lemmon (Beginning Logic [1965], 4.1)

4. Formal Logic / C. Predicate Calculus PC / 2. Tools of Predicate Calculus / b. Terminology of PC

13910	Our notation uses 'predicate-letters' (for 'properties'), 'variables', 'proper names', 'connectives' and 'quantifiers' [Lemmon]
	Full Idea: Quantifier-notation might be thus: first, render into sentences about 'properties', and use 'predicate-letters' for them; second, introduce 'variables'; third, introduce propositional logic 'connectives' and 'quantifiers'. Plus letters for 'proper names'.
	From: E.J. Lemmon (Beginning Logic [1965], 3.1)

4. Formal Logic / C. Predicate Calculus PC / 2. Tools of Predicate Calculus / c. Derivations rules of PC

13904	Universal Elimination (UE) lets us infer that an object has F, from all things having F [Lemmon]
	Full Idea: Our rule of universal quantifier elimination (UE) lets us infer that any particular object has F from the premiss that all things have F. It is a natural extension of &E (and-elimination), as universal propositions generally affirm a complex conjunction.
	From: E.J. Lemmon (Beginning Logic [1965], 3.2)

13901	Predicate logic uses propositional connectives and variables, plus new introduction and elimination rules [Lemmon]
	Full Idea: In predicate calculus we take over the propositional connectives and propositional variables - but we need additional rules for handling quantifiers: four rules, an introduction and elimination rule for the universal and existential quantifiers.
	From: E.J. Lemmon (Beginning Logic [1965])
	A reaction: This is Lemmon's natural deduction approach (invented by Gentzen), which is largely built on introduction and elimination rules.

13903	Universal elimination if you start with the universal, introduction if you want to end with it [Lemmon]
	Full Idea: The elimination rule for the universal quantifier concerns the use of a universal proposition as a premiss to establish some conclusion, whilst the introduction rule concerns what is required by way of a premiss for a universal proposition as conclusion.
	From: E.J. Lemmon (Beginning Logic [1965], 3.2)
	A reaction: So if you start with the universal, you need to eliminate it, and if you start without it you need to introduce it.

13906	With finite named objects, we can generalise with &-Intro, but otherwise we need ∀-Intro [Lemmon]
	Full Idea: If there are just three objects and each has F, then by an extension of &I we are sure everything has F. This is of no avail, however, if our universe is infinitely large or if not all objects have names. We need a new device, Universal Introduction, UI.
	From: E.J. Lemmon (Beginning Logic [1965], 3.2)

13908	UE all-to-one; UI one-to-all; EI arbitrary-to-one; EE proof-to-one [Lemmon]
	Full Idea: Univ Elim UE - if everything is F, then something is F; Univ Intro UI - if an arbitrary thing is F, everything is F; Exist Intro EI - if an arbitrary thing is F, something is F; Exist Elim EE - if a proof needed an object, there is one.
	From: E.J. Lemmon (Beginning Logic [1965], 3.3)
	A reaction: [My summary of Lemmon's four main rules for predicate calculus] This is the natural deduction approach, of trying to present the logic entirely in terms of introduction and elimination rules. See Bostock on that.

4. Formal Logic / C. Predicate Calculus PC / 2. Tools of Predicate Calculus / d. Universal quantifier ∀

13905	If there is a finite domain and all objects have names, complex conjunctions can replace universal quantifiers [Lemmon]
	Full Idea: If all objects in a given universe had names which we knew and there were only finitely many of them, then we could always replace a universal proposition about that universe by a complex conjunction.
	From: E.J. Lemmon (Beginning Logic [1965], 3.2)

4. Formal Logic / C. Predicate Calculus PC / 2. Tools of Predicate Calculus / e. Existential quantifier ∃

13900	'Some Frenchmen are generous' is rendered by (∃x)(Fx→Gx), and not with the conditional → [Lemmon]
	Full Idea: It is a common mistake to render 'some Frenchmen are generous' by (∃x)(Fx→Gx) rather than the correct (∃x)(Fx&Gx). 'All Frenchmen are generous' is properly rendered by a conditional, and true if there are no Frenchmen.
	From: E.J. Lemmon (Beginning Logic [1965], 3.1)
	A reaction: The existential quantifier implies the existence of an x, but the universal quantifier does not.

5. Theory of Logic / B. Logical Consequence / 8. Material Implication

9520	The paradoxes of material implication are P |- Q → P, and ¬P |- P → Q [Lemmon]
	Full Idea: The paradoxes of material implication are P |- Q → P, and ¬P |- P → Q. That is, since Napoleon was French, then if the moon is blue then Napoleon was French; and since Napoleon was not Chinese, then if Napoleon was Chinese, the moon is blue.
	From: E.J. Lemmon (Beginning Logic [1965], 2.2)
	A reaction: This is why the symbol → does not really mean the 'if...then' of ordinary English. Russell named it 'material implication' to show that it was a distinctively logical operator.

5. Theory of Logic / E. Structures of Logic / 4. Variables in Logic

17699	Variables are auxiliary notions, and not part of the 'eternal' essence of logic [Schönfinkel]
	Full Idea: A variable in a proposition of logic ....has the status of a mere auxiliary notion that is really inappropriate to the constant, 'eternal' essence of the propositions of logic.
	From: Moses Schönfinkel (Building Blocks of Mathematical Logic [1924], §1)
	A reaction: He presumably thinks that what the variables stand for (and he mentions 'argument places' and 'operators') will be included in the essence. My attention was caught by the thought that he takes logic to have an essence.

12. Knowledge Sources / B. Perception / 1. Perception

12581	Perceptual concepts causally influence the content of our experiences [Peacocke]
	Full Idea: Once a thinker has acquired a perceptually individuated concept, his possession of that concept can causally influence what contents his experiences possess.
	From: Christopher Peacocke (A Study of Concepts [1992], 3.3)
	A reaction: Like having 35 different words for 'snow', I suppose. I'm never convinced by such claims. Having the concepts may well influence what you look at or listen to, but I don't see the deliverances of the senses being changed by the concepts.

12. Knowledge Sources / B. Perception / 6. Inference in Perception

12579	Perception has proto-propositions, between immediate experience and concepts [Peacocke]
	Full Idea: Perceptual experience has a second layer of nonconceptual representational content, distinct from immediate 'scenarios' and from conceptual contents. These additional contents I call 'protopropositions', containing an individual and a property/relation.
	From: Christopher Peacocke (A Study of Concepts [1992], 3.3)
	A reaction: When philosophers start writing this sort of thing, I want to turn to neuroscience and psychology. I suppose the philosopher's justification for this sort of speculation is epistemological, but I see no good coming of it.

15. Nature of Minds / B. Features of Minds / 1. Consciousness / f. Higher-order thought

12586	Consciousness of a belief isn't a belief that one has it [Peacocke]
	Full Idea: I dispute the view that consciousness of a belief consists in some kind of belief that one has the belief.
	From: Christopher Peacocke (A Study of Concepts [1992], 6.2)
	A reaction: Thus if one is trying to grasp the notion of higher-order thought, it doesn't have to be just more of same but one level up. Any sensible view of the brain would suggest that one sort of activity would lead into an entirely different sort.

18. Thought / A. Modes of Thought / 6. Judgement / a. Nature of Judgement

12608	Concepts are distinguished by roles in judgement, and are thus tied to rationality [Peacocke]
	Full Idea: 'Concept' is a notion tied, in the classical Fregean manner, to cognitive significance. Concepts are distinct if we can judge rationally of one, without the other. Concepts are constitutively and definitionally tied to rationality in this way.
	From: Christopher Peacocke (Truly Understood [2008], 2.2)
	A reaction: It seems to a bit optimistic to say, more or less, that thinking is impossible if it isn't rational. Rational beings have been selected for. As Quine nicely observed, duffers at induction have all been weeded out - but they may have existed, briefly.

18. Thought / D. Concepts / 1. Concepts / b. Concepts in philosophy

18568	Philosophy should merely give necessary and sufficient conditions for concept possession [Peacocke, by Machery]
	Full Idea: Peacocke's 'Simple Account' says philosophers should determine the necessary and sufficient conditions for possessing a concept, and psychologists should explain how the human mind meets these conditions.
	From: report of Christopher Peacocke (A Study of Concepts [1992]) by Edouard Machery - Doing Without Concepts 2
	A reaction: One can't restrict philosophy so easily. Psychologists could do that job themselves, and dump philosophy. Philosophy is interested in the role of concepts in meaning, experience and judgement. If psychologists can contribute to philosophy, fine.

18571	Peacocke's account of possession of a concept depends on one view of counterfactuals [Peacocke, by Machery]
	Full Idea: Peacocke's method for discovering the possession conditions of concepts is committed to a specific account of counterfactual judgements - the Simulation Model (judgements we'd make if the antecedent were actual).
	From: report of Christopher Peacocke (A Study of Concepts [1992]) by Edouard Machery - Doing Without Concepts 2.3.4
	A reaction: Machery concludes that the Simulation Model is incorrect. This appears to be Edgington's theory of conditionals, though Machery doesn't mention her.

18572	Peacocke's account separates psychology from philosophy, and is very sketchy [Machery on Peacocke]
	Full Idea: Peacocke's Simple Account fails to connect the psychology and philosophy of concepts, it subordinates psychology to specific field of philosophy, it is committed to analytic/synthetic, and (most important) its method is very sketchy.
	From: comment on Christopher Peacocke (A Study of Concepts [1992]) by Edouard Machery - Doing Without Concepts 2.3.5
	A reaction: Machery says Peacocke proposes a research programme, and he is not surprised that no one has every followed. Machery is a well-known champion of 'experimental philosophy', makes philosophy respond to the psychology.

18. Thought / D. Concepts / 2. Origin of Concepts / a. Origin of concepts

17722	The concept 'red' is tied to what actually individuates red things [Peacocke]
	Full Idea: The possession conditions for the concept 'red' of the colour red are tied to those very conditions which individuate the colour red.
	From: Christopher Peacocke (Explaining the A Priori [2000], p.267), quoted by Carrie Jenkins - Grounding Concepts 2.5
	A reaction: Jenkins reports that he therefore argues that we can learn something about the word 'red' from thinking about the concept 'red', which is his new theory of the a priori. I find 'possession conditions' and 'individuation' to be very woolly concepts.

18. Thought / D. Concepts / 3. Ontology of Concepts / a. Concepts as representations

11127	If concepts just are mental representations, what of concepts we may never acquire? [Peacocke]
	Full Idea: We might say that the concept just is the mental representation, ...but there are concepts that human beings may never acquire. ...But if concepts are individuated by their possession conditions this will not be a problem.
	From: Christopher Peacocke (Rationale and Maxims in Study of Concepts [2005], p.169), quoted by E Margolis/S Laurence - Concepts 1.3
	A reaction: I'm not sure that I understand the notion of a concept we (or any other creature) may never acquire. They no more seem to exist than buildings that were never even designed.

18. Thought / D. Concepts / 3. Ontology of Concepts / b. Concepts as abilities

12577	Possessing a concept is being able to make judgements which use it [Peacocke]
	Full Idea: Possession of any concept requires the capacity to make judgements whose content contain it.
	From: Christopher Peacocke (A Study of Concepts [1992], 2.1)
	A reaction: Idea 12575 suggested that concept possession was an ability just to think about the concept. Why add that one must actually be able to make a judgement? Presumably to get truth in there somewhere. I may only speculate and fantasise, rather than judge.

12578	A concept is just what it is to possess that concept [Peacocke]
	Full Idea: There can be no more to a concept than is determined by a correct account of what it is to possess that concept.
	From: Christopher Peacocke (A Study of Concepts [1992], 3.2)
	A reaction: He calls this the Principle of Dependence. An odd idea, if you compare 'there is no more to a book than its possession conditions'. If the principle is right, I struggle with the proposal that a philosopher might demonstrate such a principle.

12587	Employing a concept isn't decided by introspection, but by making judgements using it [Peacocke]
	Full Idea: On the account I have been developing, what makes it the case that someone is employing one concept rather than another is not constituted by his impression of whether he is, but by complex facts about explanations of his judgements.
	From: Christopher Peacocke (A Study of Concepts [1992], 7.2)
	A reaction: I presume this brings truth into the picture, and hence establishes a link between the concept and the external world, rather than merely with other concepts. There seems to be a shadowy behaviourism lurking in the background.

18. Thought / D. Concepts / 3. Ontology of Concepts / c. Fregean concepts

12605	A sense is individuated by the conditions for reference [Peacocke]
	Full Idea: My basic Fregean idea is that a sense is individuated by the fundamental condition for something to be its reference.
	From: Christopher Peacocke (Truly Understood [2008], Intro)
	A reaction: For something to actually be its reference (as opposed to imagined reference), truth must be involved. This needs the post-1891 Frege view of such things, and not just the view of concepts as functions which he started with.

12607	Fregean concepts have their essence fixed by reference-conditions [Peacocke]
	Full Idea: The Fregean view is that the essence of a concept is given by the fundamental condition for something to be its reference.
	From: Christopher Peacocke (Truly Understood [2008], 2.1)
	A reaction: Peacocke is a supporter of the Fregean view. How does this work for concepts of odd creatures in a fantasy novel? Or for mistaken or confused concepts? For Burge's 'arthritis in my thigh'? I don't reject the Fregean view.

18. Thought / D. Concepts / 4. Structure of Concepts / a. Conceptual structure

12609	Concepts have distinctive reasons and norms [Peacocke]
	Full Idea: For each concept, there will be some reasons or norms distinctive of that concept.
	From: Christopher Peacocke (Truly Understood [2008], 2.3)
	A reaction: This is Peacocke's bold Fregean thesis (and it sounds rather Kantian to me). I dislike the word 'norms' (long story), but reasons are interesting. The trouble is the distinction between being a reason for something (its cause) and being a reason for me.

18. Thought / D. Concepts / 4. Structure of Concepts / b. Analysis of concepts

12584	An analysis of concepts must link them to something unconceptualized [Peacocke]
	Full Idea: At some point a good account of conceptual mastery must tie the mastery to abilities and relations that do not require conceptualization by the thinker.
	From: Christopher Peacocke (A Study of Concepts [1992], 5.3)
	A reaction: This obviously implies a physicalist commitment. Peacocke seeks, as so many do these days in philosophy of maths, to combine this commitment with some sort of Fregean "platonism without tears" (p.101). I don't buy it.

12604	Any explanation of a concept must involve reference and truth [Peacocke]
	Full Idea: For some particular concept, we can argue that some of its distinctive features are adequately explained only by a possession-condition that involves reference and truth essentially.
	From: Christopher Peacocke (Truly Understood [2008], Intro)
	A reaction: He reached this view via the earlier assertion that it is the role in judgement which key to understanding concepts. I like any view of such things which says that truth plays a role.

18. Thought / D. Concepts / 4. Structure of Concepts / f. Theory theory of concepts

9335	Concepts are constituted by their role in a group of propositions to which we are committed [Peacocke, by Greco]
	Full Idea: Peacocke argues that it may be a condition of possessing a certain concept that one be fundamentally committed to certain propositions which contain it. A concept is constituted by playing a specific role in the cognitive economy of its possessor.
	From: report of Christopher Peacocke (A Study of Concepts [1992]) by John Greco - Justification is not Internal §9
	A reaction: Peacocke is talking about thought and propositions rather than language. Good for him. I always have problems with this sort of view: how can something play a role if it doesn't already have intrinsic properties to make the role possible?

19. Language / B. Reference / 1. Reference theories

9336	A concept's reference is what makes true the beliefs of its possession conditions [Peacocke, by Horwich]
	Full Idea: Peacocke has a distinctive view of reference: The reference of a concept is that which will make true the primitively compelling beliefs that provide its possession conditions.
	From: report of Christopher Peacocke (A Study of Concepts [1992]) by Paul Horwich - Stipulation, Meaning and Apriority §9
	A reaction: The first thought is that there might occasionally be more than one referent which would do the job. It seems to be a very internal view of reference, where I take reference to be much more contextual and social.

19. Language / C. Assigning Meanings / 4. Compositionality

12610	Encountering novel sentences shows conclusively that meaning must be compositional [Peacocke]
	Full Idea: The phenomenon of understanding sentences one has never encountered before is decisive against theories of meaning which do not proceed compositionally.
	From: Christopher Peacocke (Truly Understood [2008], 4.3)
	A reaction: I agree entirely. It seems obvious, as soon as you begin to slowly construct a long and unusual sentence, and follow the mental processes of the listener.