23 ideas
| 2945 | Most philosophers start with reality and then examine knowledge; Descartes put the study of knowledge first [Lehrer] |
| Full Idea: Some philosophers (e.g Plato) begin with an account of reality, and then appended an account of how we can know it, ..but Descartes turned the tables, insisting that we must first decide what we can know. | |
| From: Keith Lehrer (Theory of Knowledge (2nd edn) [2000], I p.2) |
| 2946 | You cannot demand an analysis of a concept without knowing the purpose of the analysis [Lehrer] |
| Full Idea: An analysis is always relative to some objective. It makes no sense to simply demand an analysis of goodness, knowledge, beauty or truth, without some indication of the purpose of the analysis. | |
| From: Keith Lehrer (Theory of Knowledge (2nd edn) [2000], I p.7) | |
| A reaction: Your dismantling of a car will go better if you know what a car is for, but you can still take it apart in ignorance. |
| 13030 | Extensionality: ∀x ∀y (∀z (z ∈ x ↔ z ∈ y) → x = y) [Kunen] |
| Full Idea: Axiom of Extensionality: ∀x ∀y (∀z (z ∈ x ↔ z ∈ y) → x = y). That is, a set is determined by its members. If every z in one set is also in the other set, then the two sets are the same. | |
| From: Kenneth Kunen (Set Theory [1980], §1.5) |
| 13032 | Pairing: ∀x ∀y ∃z (x ∈ z ∧ y ∈ z) [Kunen] |
| Full Idea: Axiom of Pairing: ∀x ∀y ∃z (x ∈ z ∧ y ∈ z). Any pair of entities must form a set. | |
| From: Kenneth Kunen (Set Theory [1980], §1.6) | |
| A reaction: Repeated applications of this can build the hierarchy of sets. |
| 13033 | Union: ∀F ∃A ∀Y ∀x (x ∈ Y ∧ Y ∈ F → x ∈ A) [Kunen] |
| Full Idea: Axiom of Union: ∀F ∃A ∀Y ∀x (x ∈ Y ∧ Y ∈ F → x ∈ A). That is, the union of a set (all the members of the members of the set) must also be a set. | |
| From: Kenneth Kunen (Set Theory [1980], §1.6) |
| 13037 | Infinity: ∃x (0 ∈ x ∧ ∀y ∈ x (S(y) ∈ x) [Kunen] |
| Full Idea: Axiom of Infinity: ∃x (0 ∈ x ∧ ∀y ∈ x (S(y) ∈ x). That is, there is a set which contains zero and all of its successors, hence all the natural numbers. The principal of induction rests on this axiom. | |
| From: Kenneth Kunen (Set Theory [1980], §1.7) |
| 13038 | Power Set: ∀x ∃y ∀z(z ⊂ x → z ∈ y) [Kunen] |
| Full Idea: Power Set Axiom: ∀x ∃y ∀z(z ⊂ x → z ∈ y). That is, there is a set y which contains all of the subsets of a given set. Hence we define P(x) = {z : z ⊂ x}. | |
| From: Kenneth Kunen (Set Theory [1980], §1.10) |
| 13034 | Replacement: ∀x∈A ∃!y φ(x,y) → ∃Y ∀X∈A ∃y∈Y φ(x,y) [Kunen] |
| Full Idea: Axiom of Replacement Scheme: ∀x ∈ A ∃!y φ(x,y) → ∃Y ∀X ∈ A ∃y ∈ Y φ(x,y). That is, any function from a set A will produce another set Y. | |
| From: Kenneth Kunen (Set Theory [1980], §1.6) |
| 13039 | Foundation:∀x(∃y(y∈x) → ∃y(y∈x ∧ ¬∃z(z∈x ∧ z∈y))) [Kunen] |
| Full Idea: Axiom of Foundation: ∀x (∃y(y ∈ x) → ∃y(y ∈ x ∧ ¬∃z(z ∈ x ∧ z ∈ y))). Aka the 'Axiom of Regularity'. Combined with Choice, it means there are no downward infinite chains. | |
| From: Kenneth Kunen (Set Theory [1980], §3.4) |
| 13036 | Choice: ∀A ∃R (R well-orders A) [Kunen] |
| Full Idea: Axiom of Choice: ∀A ∃R (R well-orders A). That is, for every set, there must exist another set which imposes a well-ordering on it. There are many equivalent versions. It is not needed in elementary parts of set theory. | |
| From: Kenneth Kunen (Set Theory [1980], §1.6) |
| 13029 | Set Existence: ∃x (x = x) [Kunen] |
| Full Idea: Axiom of Set Existence: ∃x (x = x). This says our universe is non-void. Under most developments of formal logic, this is derivable from the logical axioms and thus redundant, but we do so for emphasis. | |
| From: Kenneth Kunen (Set Theory [1980], §1.5) |
| 13031 | Comprehension: ∃y ∀x (x ∈ y ↔ x ∈ z ∧ φ) [Kunen] |
| Full Idea: Comprehension Scheme: for each formula φ without y free, the universal closure of this is an axiom: ∃y ∀x (x ∈ y ↔ x ∈ z ∧ φ). That is, there must be a set y if it can be defined by the formula φ. | |
| From: Kenneth Kunen (Set Theory [1980], §1.5) | |
| A reaction: Unrestricted comprehension leads to Russell's paradox, so restricting it in some way (e.g. by the Axiom of Specification) is essential. |
| 13040 | Constructibility: V = L (all sets are constructible) [Kunen] |
| Full Idea: Axiom of Constructability: this is the statement V = L (i.e. ∀x ∃α(x ∈ L(α)). That is, the universe of well-founded von Neumann sets is the same as the universe of sets which are actually constructible. A possible axiom. | |
| From: Kenneth Kunen (Set Theory [1980], §6.3) |
| 12797 | If plural variables have 'some values', then non-count variables have 'some value' [Laycock] |
| Full Idea: If a plural variable is said to have not a single value but some values (some clothes), then a non-count variable may have, more quirkier still, some value (some clothing, for instance) in ranging arbitrarily over the scattered stuff. | |
| From: Henry Laycock (Words without Objects [2006], 4.4) | |
| A reaction: We seem to need the notion of a sample, or an archetype, to fit the bill. I hereby name them 'sample variables'. Damn - Laycock got there first, on p.137. |
| 12794 | Plurals are semantical but not ontological [Laycock] |
| Full Idea: Plurality is a semantical but not also an ontological construction. | |
| From: Henry Laycock (Words without Objects [2006], Intro 4) | |
| A reaction: I love it when philososphers make simple and illuminating remarks like this. You could read 500 pages of technical verbiage about plural reference without grasping that this is the underlying issue. Sounds right to me. |
| 17694 | Some non-count nouns can be used for counting, as in 'several wines' or 'fewer cheeses' [Laycock] |
| Full Idea: The very words we class as non-count nouns may themselves be used for counting, of kinds or types, and phrases like 'several wines' are perfectly in order. ...Not only do we have 'less cheese', but we also have the non-generic 'fewer cheeses'. | |
| From: Henry Laycock (Words without Objects [2006], Intro 4 n23) | |
| A reaction: [compressed] Laycock generally endorses the thought that what can be counted is not simply distinguished by a precise class of applied vocabulary. He offers lots of borderline or ambiguous cases in his footnotes. |
| 17695 | Some apparent non-count words can take plural forms, such as 'snows' or 'waters' [Laycock] |
| Full Idea: Some words that seem to be semantically non-count can take syntactically plural forms: 'snows', 'sands', 'waters' and the like. | |
| From: Henry Laycock (Words without Objects [2006], Intro 4 n24) | |
| A reaction: This seems to involve parcels of the stuff. The 'snows of yesteryear' occur at different times. 'Taking the waters' probably involves occasions. The 'Arabian sands' presumably occur in different areas. Semantics won't fix what is countable. |
| 12792 | The category of stuff does not suit reference [Laycock] |
| Full Idea: The central fact about the category of stuff or matter is that it is profoundly antithetical to reference. | |
| From: Henry Laycock (Words without Objects [2006], Pref) | |
| A reaction: This is taking 'reference' in the strictly singular classical sense, but clearly we refer to water in various ways. Laycock's challenge is very helpful. We have been in the grips of a terrible orthodoxy. |
| 12799 | Descriptions of stuff are neither singular aggregates nor plural collections [Laycock] |
| Full Idea: The definite descriptions of stuff like water are neither singular descriptions denoting individual mereological aggregates, nor plural descriptions denoting multitudes of discrete units or semantically determined atoms. | |
| From: Henry Laycock (Words without Objects [2006], 5.3) | |
| A reaction: Laycock makes an excellent case for this claim, and seems to invite a considerable rethink of our basic ontology to match it, one which he ultimately hints at calling 'romantic'. Nice. Conservatives try to force stuff into classical moulds. |
| 12818 | We shouldn't think some water retains its identity when it is mixed with air [Laycock] |
| Full Idea: Suppose that water, qua vapour, mixes with the atmosphere. Is there any abstract metaphysical principle, other than that of atomism, which implies that water must, in any such process, retain its identity? That claim seems indefensible. | |
| From: Henry Laycock (Words without Objects [2006], 1.2 n22) | |
| A reaction: It can't be right that some stuff always loses its identity in a mixture, if the mixture was in a closed vessel, and then separated again. Dispersion is what destroys the identity, not mixing. |
| 12795 | Parts must be of the same very general type as the wholes [Laycock] |
| Full Idea: The notion of a part is such that parts must be of the same very general type - concrete, material or physical, for instance - as the wholes of which they are (said to be) parts. | |
| From: Henry Laycock (Words without Objects [2006], 2.9) | |
| A reaction: The phrase 'same very general type' cries out for investigation. Can an army contain someone who isn't much of a soldier? Can the Treasury contain a fear of inflation? |
| 17696 | 'Humility is a virtue' has an abstract noun, but 'water is a liquid' has a generic concrete noun [Laycock] |
| Full Idea: Work is needed to distinguish abstract nouns ...from the generic uses of what are otherwise concrete nouns. The contrast is that of 'humility is a virtue' and 'water is a liquid'. | |
| From: Henry Laycock (Words without Objects [2006], Intro 4 n25) | |
| A reaction: 'Work is needed' implies 'let me through, I'm an analytic philosopher', but I don't think they will separate very easily. What does 'watery' mean? Does water have concrete virtues? |
| 12791 | It is said that proper reference is our intellectual link with the world [Laycock] |
| Full Idea: Some people hold that it is reference, in some more or less full-blooded sense, which constitutes our basic intellectual or psychological connection with the world. | |
| From: Henry Laycock (Words without Objects [2006], Pref) | |
| A reaction: This is the view which Laycock sets out to challenge, by showing that we talk about stuff like water without any singular reference occurring at all. I think he is probably right. |