21 ideas
| 11178 | The essence or definition of an essence involves either a class of properties or a class of propositions [Fine,K] |
| Full Idea: If each object has a unique essence or definition, this may be identified with either the class of properties that it essentially has, or with the class of propositions that are true in virtue of what it is. | |
| From: Kit Fine (Senses of Essence [1995], §8) | |
| A reaction: Elsewhere Fine says that it is easier to work with the propositions view, but that the properties (or predicates) view is probably more fundamental. He goes on here to raise the question of whether either view makes the essence unique. |
| 10301 | The axiom of choice is controversial, but it could be replaced [Shapiro] |
| Full Idea: The axiom of choice has a troubled history, but is now standard in mathematics. It could be replaced with a principle of comprehension for functions), or one could omit the variables ranging over functions. | |
| From: Stewart Shapiro (Higher-Order Logic [2001], n 3) |
| 10588 | First-order logic is Complete, and Compact, with the Löwenheim-Skolem Theorems [Shapiro] |
| Full Idea: Early study of first-order logic revealed a number of important features. Gödel showed that there is a complete, sound and effective deductive system. It follows that it is Compact, and there are also the downward and upward Löwenheim-Skolem Theorems. | |
| From: Stewart Shapiro (Higher-Order Logic [2001], 2.1) |
| 10298 | Some say that second-order logic is mathematics, not logic [Shapiro] |
| Full Idea: Some authors argue that second-order logic (with standard semantics) is not logic at all, but is a rather obscure form of mathematics. | |
| From: Stewart Shapiro (Higher-Order Logic [2001], 2.4) |
| 10299 | If the aim of logic is to codify inferences, second-order logic is useless [Shapiro] |
| Full Idea: If the goal of logical study is to present a canon of inference, a calculus which codifies correct inference patterns, then second-order logic is a non-starter. | |
| From: Stewart Shapiro (Higher-Order Logic [2001], 2.4) | |
| A reaction: This seems to be because it is not 'complete'. However, moves like plural quantification seem aimed at capturing ordinary language inferences, so the difficulty is only that there isn't a precise 'calculus'. |
| 10300 | Logical consequence can be defined in terms of the logical terminology [Shapiro] |
| Full Idea: Informally, logical consequence is sometimes defined in terms of the meanings of a certain collection of terms, the so-called 'logical terminology'. | |
| From: Stewart Shapiro (Higher-Order Logic [2001], 2.4) | |
| A reaction: This seems to be a compositional account, where we build a full account from an account of the atomic bits, perhaps presented as truth-tables. |
| 11175 | Logical concepts rest on certain inferences, not on facts about implications [Fine,K] |
| Full Idea: The nature of the logical concepts is given, not by certain logical truths, but by certain logical inferences. What properly belongs to disjunction is the inference from p to (p or q), rather than the fact that p implies (p or q). | |
| From: Kit Fine (Senses of Essence [1995], §3) | |
| A reaction: Does this mean that Fine is wickedly starting with the psychology, rather than with the pure truth of the connection? Frege is shuddering. This view seems to imply that the truth table for 'or' is secondary. |
| 11176 | The property of Property Abstraction says any suitable condition must imply a property [Fine,K] |
| Full Idea: According to the principle of Property Abstraction, there is, for any suitable condition, a property that is possessed by an object just in case it conforms to the condition. This is usually taken to be a second-order logical truth. | |
| From: Kit Fine (Senses of Essence [1995], §4) | |
| A reaction: Fine objects that it is implied that if Socrates is essentially a man, then he essentially has the property of being a man. Like Fine, I think this conclusion is distasteful. A classification is not a property, at least the way most people use 'property'. |
| 10290 | Second-order variables also range over properties, sets, relations or functions [Shapiro] |
| Full Idea: Second-order variables can range over properties, sets, or relations on the items in the domain-of-discourse, or over functions from the domain itself. | |
| From: Stewart Shapiro (Higher-Order Logic [2001], 2.1) |
| 11174 | A logical truth is true in virtue of the nature of the logical concepts [Fine,K] |
| Full Idea: One wants to define a logical truth as one that is true in virtue of the nature of the logical concepts. | |
| From: Kit Fine (Senses of Essence [1995], §3) | |
| A reaction: This is part of Fine's project to give a revised account of essence, which includes the essence of concepts as well as the essence of objects. Everyone should pay close attention to this project. |
| 10292 | Downward Löwenheim-Skolem: if there's an infinite model, there is a countable model [Shapiro] |
| Full Idea: Downward Löwenheim-Skolem: a finite or denumerable set of first-order formulas that is satisfied by a model whose domain is infinite is satisfied in a model whose domain is the natural numbers | |
| From: Stewart Shapiro (Higher-Order Logic [2001], 2.1) |
| 10590 | Up Löwenheim-Skolem: if natural numbers satisfy wffs, then an infinite domain satisfies them [Shapiro] |
| Full Idea: Upward Löwenheim-Skolem: if a set of first-order formulas is satisfied by a domain of at least the natural numbers, then it is satisfied by a model of at least some infinite cardinal. | |
| From: Stewart Shapiro (Higher-Order Logic [2001], 2.1) |
| 10296 | The Löwenheim-Skolem Theorems fail for second-order languages with standard semantics [Shapiro] |
| Full Idea: Both of the Löwenheim-Skolem Theorems fail for second-order languages with a standard semantics | |
| From: Stewart Shapiro (Higher-Order Logic [2001], 2.3.2) |
| 10297 | The Löwenheim-Skolem theorem seems to be a defect of first-order logic [Shapiro] |
| Full Idea: The Löwenheim-Skolem theorem is usually taken as a sort of defect (often thought to be inevitable) of the first-order logic. | |
| From: Stewart Shapiro (Higher-Order Logic [2001], 2.4) | |
| A reaction: [He is quoting Wang 1974 p.154] |
| 10294 | Second-order logic has the expressive power for mathematics, but an unworkable model theory [Shapiro] |
| Full Idea: Full second-order logic has all the expressive power needed to do mathematics, but has an unworkable model theory. | |
| From: Stewart Shapiro (Higher-Order Logic [2001], 2.1) | |
| A reaction: [he credits Cowles for this remark] Having an unworkable model theory sounds pretty serious to me, as I'm not inclined to be interested in languages which don't produce models of some sort. Surely models are the whole point? |
| 10591 | Logicians use 'property' and 'set' interchangeably, with little hanging on it [Shapiro] |
| Full Idea: In studying second-order logic one can think of relations and functions as extensional or intensional, or one can leave it open. Little turns on this here, and so words like 'property', 'class', and 'set' are used interchangeably. | |
| From: Stewart Shapiro (Higher-Order Logic [2001], 2.2.1) | |
| A reaction: Important. Students of the metaphysics of properties, who arrive with limited experience of logic, are bewildered by this attitude. Note that the metaphysics is left wide open, so never let logicians hijack the metaphysical problem of properties. |
| 11177 | Can the essence of an object circularly involve itself, or involve another object? [Fine,K] |
| Full Idea: Can the essence of an object (ineliminably) involve that object itself (perhaps through self-identity, giving a direct circularity), or have an indirect circularity involving two or more objects (such as admiration between Watson and Holmes). | |
| From: Kit Fine (Senses of Essence [1995], §7) | |
| A reaction: [compressed] This looks like one of the basic questions which any theory of essentialism must address. |
| 11173 | Being a man is a consequence of his essence, not constitutive of it [Fine,K] |
| Full Idea: If we distinguish 'constitutive' from 'consequential' essence, ..then the essence of Socrates will, in part, be constituted by his being a man. But being a man (or a mountain) will merely be consequential upon, and not constitutive of, his essence. | |
| From: Kit Fine (Senses of Essence [1995], §3) | |
| A reaction: Yes yes yes. I think it is absurd to say that the class to which something belongs is part of its essential nature, given that it presumably can only belong to the class if it already has a certain essential nature. What did Frankenstein construct? |
| 11179 | If there are alternative definitions, then we have three possibilities for essence [Fine,K] |
| Full Idea: If there are alternative definitions for an essence, we must distinguish three notions. There is the essence as the manifold (the combined definitions), or as the range of alternative definitions (with component essences), or there is the common essence. | |
| From: Kit Fine (Senses of Essence [1995], §8) | |
| A reaction: Fine opts for the third alternative (what the definitions all have in common) as the best account. He says (p.68) 'definitive' properties come from one definition, and 'essential' properties from every possible definition. |
| 1748 | Archelaus was the first person to say that the universe is boundless [Archelaus, by Diog. Laertius] |
| Full Idea: Archelaus was the first person to say that the universe is boundless. | |
| From: report of Archelaus (fragments/reports [c.450 BCE]) by Diogenes Laertius - Lives of Eminent Philosophers 02.Ar.3 |
| 5989 | Archelaus said life began in a primeval slime [Archelaus, by Schofield] |
| Full Idea: Archelaus wrote that life on Earth began in a primeval slime. | |
| From: report of Archelaus (fragments/reports [c.450 BCE]) by Malcolm Schofield - Archelaus | |
| A reaction: This sounds like a fairly clearcut assertion of the production of life by evolution. Darwin's contribution was to propose the mechanism for achieving it. We should honour the name of Archelaus for this idea. |