Ideas from 'The Metaphysics of Modality' by Graeme Forbes [1985], by Theme Structure

[found in 'The Metaphysics of Modality' by Forbes,Graeme [OUP 1985,0-19-824432-0]].

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1. Philosophy / E. Nature of Metaphysics / 2. Possibility of Metaphysics
There must be a plausible epistemological theory alongside any metaphysical theory
                        Full Idea: No metaphysical account which renders it impossible to give a plausible epistemological theory is to be countenanced.
                        From: Graeme Forbes (The Metaphysics of Modality [1985], 9.1)
                        A reaction: It is hard to object to this principle, though we certainly don't want to go verificationist, and thus rule out speculations about metaphysics which are beyond any possible knowledge. Some have tried to prove that something must exist (e.g. Jacquette).
4. Formal Logic / B. Propositional Logic PL / 2. Tools of Propositional Logic / a. Symbols of PL
The symbol 'ι' forms definite descriptions; (ιx)F(x) says 'the x which is such that F(x)'
                        Full Idea: We use the symbol 'ι' (Greek 'iota') to form definite descriptions, reading (ιx)F(x) as 'the x which is such that F(x)', or simply as 'the F'.
                        From: Graeme Forbes (The Metaphysics of Modality [1985], 4.1)
                        A reaction: Compare the lambda operator in modal logic, which picks out predicates from similar formulae.
5. Theory of Logic / E. Structures of Logic / 2. Logical Connectives / d. and
Is the meaning of 'and' given by its truth table, or by its introduction and elimination rules?
                        Full Idea: The typical semantic account of validity for propositional connectives like 'and' presupposes that meaning is given by truth-tables. On the natural deduction view, the meaning of 'and' is given by its introduction and elimination rules.
                        From: Graeme Forbes (The Metaphysics of Modality [1985], 4.4)
7. Existence / D. Theories of Reality / 9. Vagueness / d. Vagueness as linguistic
Vagueness problems arise from applying sharp semantics to vague languages
                        Full Idea: It is very plausible that the sorites paradoxes arose from the application of a semantic apparatus appropriate only for sharp predicates to languages containing vague predicates (rather than from deficiency of meaning, or from incoherence).
                        From: Graeme Forbes (The Metaphysics of Modality [1985], 7.3)
                        A reaction: Sounds wrong. Of course, logic has been designed for sharp predicates, and natural languages are awash with vagueness. But the problems of vagueness bothered lawyers long before logicians like Russell began to worry about it.
9. Objects / A. Existence of Objects / 5. Individuation / a. Individuation
In all instances of identity, there must be some facts to ensure the identity
                        Full Idea: For each instance of identity or failure of identity, there must be facts in virtue of which that instance obtains. ..Enough has been said to lend this doctrine some plausibility.
                        From: Graeme Forbes (The Metaphysics of Modality [1985], 5.5)
                        A reaction: Penelope Mackie picks this out from Forbes as a key principle. It sounds to be in danger of circularity, unless the 'facts' can be cited without referring to, or implicitly making use of, identities - which seems unlikely.
9. Objects / B. Unity of Objects / 3. Unity Problems / d. Coincident objects
If we combined two clocks, it seems that two clocks may have become one clock.
                        Full Idea: If we imagine a possible world in which two clocks in a room make one clock from half the parts of each, the judgement 'these two actual clocks could have been a single clock' does not seem wholly false.
                        From: Graeme Forbes (The Metaphysics of Modality [1985], 7.4)
                        A reaction: You would, of course, have sufficient parts left over to make a second clock, so they look like a destroyed clock, so I don't think I find Forbes's intuition on this one very persuasive.
9. Objects / D. Essence of Objects / 3. Individual Essences
Only individual essences will ground identities across worlds in other properties
                        Full Idea: Forbes argues that, unless we posit individual essences, we cannot guarantee that identities across possible worlds will be appropriately grounded in other properties.
                        From: report of Graeme Forbes (The Metaphysics of Modality [1985]) by Penelope Mackie - How Things Might Have Been 2.4
                        A reaction: There is a confrontation between Wiggins, who says identity is primitive, and Forbes, who says identity must be grounded in other properties. I think I side with Forbes.
An individual essence is a set of essential properties which only that object can have
                        Full Idea: An individual essence of an object x is a set of properties I which satisfies the following conditions: i. every property P in I is an essential property of x; ii. it is not possible that some object y distinct from x has every member of I.
                        From: Graeme Forbes (The Metaphysics of Modality [1985], 5.1)
                        A reaction: I am coming to the view that stable natural kinds (like electrons or gold) do not have individual essences, but complex kinds (like tigers or tables) do. The view is based on the idea that explanatory power is what individuates an essence.
Non-trivial individual essence is properties other than de dicto, or universal, or relational
                        Full Idea: A non-trivial individual essence is properties other than a) those following from a de dicto truth, b) properties of existence and self-identity (or their cognates), c) properties derived from necessities in some other category.
                        From: Graeme Forbes (The Metaphysics of Modality [1985], 5.1)
                        A reaction: [I have compressed Forbes] Rather than adding all these qualificational clauses to our concept, we could just tighten up on the notion of a property, saying it is something which is causally efficacious, and hence explanatory.
9. Objects / D. Essence of Objects / 5. Essence as Kind
Essential properties depend on a category, and perhaps also on particular facts
                        Full Idea: The essential properties of a thing will typically depend upon what category of thing it is, and perhaps also on some more particular facts about the thing itself.
                        From: Graeme Forbes (The Metaphysics of Modality [1985], 5.1)
                        A reaction: I see no way of dispensing with the second requirement, in the cases of complex entities like animals. If all samples are the same, then of course we can define a sample's essence through its kind, but not if samples differ in any way.
9. Objects / D. Essence of Objects / 7. Essence and Necessity / a. Essence as necessary properties
Essential properties are those without which an object could not exist
                        Full Idea: An essential property of an object x is a property without possessing which x could not exist.
                        From: Graeme Forbes (The Metaphysics of Modality [1985], 5.1)
                        A reaction: This is certainly open to question. See Joan Kung's account of Aristotle on essence. I am necessarily more than eight years old (now), and couldn't exist without that property, but is the property part of my essence?
9. Objects / D. Essence of Objects / 11. Essence of Artefacts
Artefacts have fuzzy essences
                        Full Idea: Artefacts can be ascribed fuzzy essences. ...We might say that it is essential to an artefact to have 'most' of its parts.
                        From: Graeme Forbes (The Metaphysics of Modality [1985], 7.6)
                        A reaction: I think I prefer to accept the idea that essences are unstable things, in all cases. For all we know, electrons might subtly change their general character, or cease to be uniform, tomorrow. Essences explain, and what needs explaining changes.
Same parts does not ensure same artefact, if those parts could constitute a different artefact
                        Full Idea: Sameness of parts is not sufficient for identity of artefacts at a world, since the very same parts may turn up at different times as the parts of artefacts with different designs and functions.
                        From: Graeme Forbes (The Metaphysics of Modality [1985], 7.2)
                        A reaction: Thus the Ship of Theseus could be dismantled and turned into a barn (as happened with the 'Mayflower'). They could then be reconstituted as the ship, which would then have two beginnings (as Chris Hughes has pointed out).
9. Objects / E. Objects over Time / 12. Origin as Essential
An individual might change their sex in a world, but couldn't have differed in sex at origin
                        Full Idea: In the time of a single world, the same individual can undergo a change of sex, but it is less clear that an individual of one sex could have been, from the outset, an individual of another.
                        From: Graeme Forbes (The Metaphysics of Modality [1985], 6.5)
                        A reaction: I don't find this support for essentiality of origin very persuasive. I struggle with these ideas. Given my sex yesterday, then presumably I couldn't have had a different sex yesterday. Given that pigs can fly, pigs can fly. What am I missing?
9. Objects / F. Identity among Objects / 1. Concept of Identity
Identities must hold because of other facts, which must be instrinsic
                        Full Idea: Forbes has two principles of identity, which we can call the No Bare Identities Principle (identities hold in virtue of other facts), and the No Extrinsic Determination Principle (that only intrinsic facts of a thing establish identity).
                        From: report of Graeme Forbes (The Metaphysics of Modality [1985], 127-8) by Penelope Mackie - How Things Might Have Been 2.7
                        A reaction: The job of the philosopher is to prise apart the real identities of things from the way in which we conceive of identities. I take these principles to apply to real identities, not conceptual identities.
10. Modality / A. Necessity / 4. De re / De dicto modality
De re modal formulae, unlike de dicto, are sensitive to transworld identities
                        Full Idea: The difference between de re and de dicto formulae is a difference between formulae which are, and formulae which are not, sensitive to the identities of objects at various worlds.
                        From: Graeme Forbes (The Metaphysics of Modality [1985], 3.1)
10. Modality / C. Sources of Modality / 4. Necessity from Concepts
De re necessity is a form of conceptual necessity, just as de dicto necessity is
                        Full Idea: De re necessity does not differ from de dicto necessity in respect of how it arises: it is still a form of conceptual necessity.
                        From: Graeme Forbes (The Metaphysics of Modality [1985], 9.4)
                        A reaction: [Forbes proceeds to argue for this claim] Forbes defends a form of essentialism, but takes the necessity to arise from a posteriori truths because of the a priori involvement of other concepts (rather as Kripke argues).
10. Modality / E. Possible worlds / 1. Possible Worlds / c. Possible worlds realism
Unlike places and times, we cannot separate possible worlds from what is true at them
                        Full Idea: There is no means by which we might distinguish a possible world from what is true at it. ...Whereas our ability to separate a place, or a time, from its occupier is crucial to realism about places and times, as is a distance relation.
                        From: Graeme Forbes (The Metaphysics of Modality [1985], 4.2)
                        A reaction: He is objecting to Lewis's modal realism. I'm not fully convinced. It depends whether we are discussing real ontology or conceptual space. In the latter I see no difference between times and possible worlds. In ontology, a 'time' is weird.
The problem with possible worlds realism is epistemological; we can't know properties of possible objects
                        Full Idea: The main objection to realism about worlds is from epistemology. Knowledge of properties of objects requires experience of these objects, which must be within the range of our sensory faculties, but only concrete actual objects achieve that.
                        From: Graeme Forbes (The Metaphysics of Modality [1985], 4.2)
                        A reaction: This pinpoints my dislike of the whole possible worlds framework, ontologically speaking. I seem to be an actualist. I take possibilities to be inferences to the best explanation from the powers we know of in the actual world. We experience potentiality.
10. Modality / E. Possible worlds / 2. Nature of Possible Worlds / a. Nature of possible worlds
Possible worlds are points of logical space, rather like other times than our own
                        Full Idea: Someone impressed by the parallel between tense and modal operators ...might suggest that just as we can speak of places and times forming their own manifolds or spaces, so we can say that worlds are the points of logical space.
                        From: Graeme Forbes (The Metaphysics of Modality [1985], 4.2)
                        A reaction: I particularly like the notion of worlds being "points of logical space", and am inclined to remove it from this context and embrace it as the correct way to understand possible worlds. We must understand logical or conceptual space.
10. Modality / E. Possible worlds / 3. Transworld Objects / a. Transworld identity
Transworld identity concerns the limits of possibility for ordinary things
                        Full Idea: An elucidation of transworld identity can be regarded as an elucidation of the boundaries of possibility for ordinary things.
                        From: Graeme Forbes (The Metaphysics of Modality [1985], 5.1)
                        A reaction: I presume that if we don't search for some such criterion, we just have to face the possibility that Aristotle could have been a poached egg in some possible world. To know the bounds of possibility, study the powers of actual objects.
The problem of transworld identity can be solved by individual essences
                        Full Idea: The motivation for investigating individual essences should be obvious, since if every object has such an essence, the problem of elucidating transworld identity can be solved.
                        From: Graeme Forbes (The Metaphysics of Modality [1985], 5.1)
                        A reaction: It is important that, if necessary, the identities be 'individual', and not just generic, by sortal, or natural kind. We want to reason about (and explain) truths at the fine-grained level of the individual, not just at the broad level of generalisation.
10. Modality / E. Possible worlds / 3. Transworld Objects / c. Counterparts
Counterpart theory is not good at handling the logic of identity
                        Full Idea: The outstanding technical objection to counterpart-theoretic semantics concerns its handling of the logic of identity. In quantified S5 (the orthodox semantics) a = b → □(a = b) is valid, but 'a' must not attach to two objects.
                        From: Graeme Forbes (The Metaphysics of Modality [1985], 3.5)
10. Modality / E. Possible worlds / 3. Transworld Objects / d. Haecceitism
Haecceitism attributes to each individual a primitive identity or thisness
                        Full Idea: Haecceitism attributes to each individual a primitive identity or thisness, as opposed to the sort of essentialism that gives non-trivial conditions sufficient for transworld identity.
                        From: Graeme Forbes (The Metaphysics of Modality [1985], 6.6)
                        A reaction: 'Haecceitism' is the doctrine that things have primitive identity. A 'haecceity' is a postulated property which actually does the job. The key point of the view is that whatever it is is 'primitive', and not complex, or analysable. I don't believe it.
We believe in thisnesses, because we reject bizarre possibilities as not being about that individual
                        Full Idea: The natural response to an unreasonable hypothesis of possibility for an object x, that in such a state of affairs it would not be x which satisfies the conditions, is evidence that we do possess concepts of thisness for individuals.
                        From: Graeme Forbes (The Metaphysics of Modality [1985], 9.4)
                        A reaction: We may have a 'concept' of thisness, but we needn't be committed to the 'existence' of a thisness. There is a fairly universal intuition that cessation of existence of an entity when it starts to change can be a very vague matter.