34 ideas
9724 | Until the 1960s the only semantics was truth-tables [Enderton] |
Full Idea: Until the 1960s standard truth-table semantics were the only ones that there were. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], 1.10.1) | |
A reaction: The 1960s presumably marked the advent of possible worlds. |
9703 | 'dom R' indicates the 'domain' of objects having a relation [Enderton] |
Full Idea: 'dom R' indicates the 'domain' of a relation, that is, the set of all objects that are members of ordered pairs and that have that relation. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
9705 | 'fld R' indicates the 'field' of all objects in the relation [Enderton] |
Full Idea: 'fld R' indicates the 'field' of a relation, that is, the set of all objects that are members of ordered pairs on either side of the relation. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
9704 | 'ran R' indicates the 'range' of objects being related to [Enderton] |
Full Idea: 'ran R' indicates the 'range' of a relation, that is, the set of all objects that are members of ordered pairs and that are related to by the first objects. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
9710 | We write F:A→B to indicate that A maps into B (the output of F on A is in B) [Enderton] |
Full Idea: We write F : A → B to indicate that A maps into B, that is, the domain of relating things is set A, and the things related to are all in B. If we add that F = B, then A maps 'onto' B. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
9707 | 'F(x)' is the unique value which F assumes for a value of x [Enderton] |
Full Idea:
F(x) is a 'function', which indicates the unique value which y takes in |
|
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
9712 | A relation is 'symmetric' on a set if every ordered pair has the relation in both directions [Enderton] |
Full Idea: A relation is 'symmetric' on a set if every ordered pair in the set has the relation in both directions. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
9713 | A relation is 'transitive' if it can be carried over from two ordered pairs to a third [Enderton] |
Full Idea: A relation is 'transitive' on a set if the relation can be carried over from two ordered pairs to a third. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
9699 | The 'powerset' of a set is all the subsets of a given set [Enderton] |
Full Idea: The 'powerset' of a set is all the subsets of a given set. Thus: PA = {x : x ⊆ A}. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
9700 | Two sets are 'disjoint' iff their intersection is empty [Enderton] |
Full Idea: Two sets are 'disjoint' iff their intersection is empty (i.e. they have no members in common). | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
9702 | A 'domain' of a relation is the set of members of ordered pairs in the relation [Enderton] |
Full Idea: The 'domain' of a relation is the set of all objects that are members of ordered pairs that are members of the relation. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
9701 | A 'relation' is a set of ordered pairs [Enderton] |
Full Idea: A 'relation' is a set of ordered pairs. The ordering relation on the numbers 0-3 is captured by - in fact it is - the set of ordered pairs {<0,1>,<0,2>,<0,3>,<1,2>,<1,3>,<2,3>}. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) | |
A reaction: This can't quite be a definition of order among numbers, since it relies on the notion of a 'ordered' pair. |
9706 | A 'function' is a relation in which each object is related to just one other object [Enderton] |
Full Idea: A 'function' is a relation which is single-valued. That is, for each object, there is only one object in the function set to which that object is related. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
9708 | A function 'maps A into B' if the relating things are set A, and the things related to are all in B [Enderton] |
Full Idea: A function 'maps A into B' if the domain of relating things is set A, and the things related to are all in B. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
9709 | A function 'maps A onto B' if the relating things are set A, and the things related to are set B [Enderton] |
Full Idea: A function 'maps A onto B' if the domain of relating things is set A, and the things related to are set B. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
9711 | A relation is 'reflexive' on a set if every member bears the relation to itself [Enderton] |
Full Idea: A relation is 'reflexive' on a set if every member of the set bears the relation to itself. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
9714 | A relation satisfies 'trichotomy' if all pairs are either relations, or contain identical objects [Enderton] |
Full Idea: A relation satisfies 'trichotomy' on a set if every ordered pair is related (in either direction), or the objects are identical. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
9717 | A set is 'dominated' by another if a one-to-one function maps the first set into a subset of the second [Enderton] |
Full Idea: A set is 'dominated' by another if a one-to-one function maps the first set into a subset of the second. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
9715 | An 'equivalence relation' is a reflexive, symmetric and transitive binary relation [Enderton] |
Full Idea: An 'equivalence relation' is a binary relation which is reflexive, and symmetric, and transitive. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
9716 | We 'partition' a set into distinct subsets, according to each relation on its objects [Enderton] |
Full Idea: Equivalence classes will 'partition' a set. That is, it will divide it into distinct subsets, according to each relation on the set. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
9722 | Inference not from content, but from the fact that it was said, is 'conversational implicature' [Enderton] |
Full Idea: The process is dubbed 'conversational implicature' when the inference is not from the content of what has been said, but from the fact that it has been said. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], 1.7.3) |
9718 | Validity is either semantic (what preserves truth), or proof-theoretic (following procedures) [Enderton] |
Full Idea: The point of logic is to give an account of the notion of validity,..in two standard ways: the semantic way says that a valid inference preserves truth (symbol |=), and the proof-theoretic way is defined in terms of purely formal procedures (symbol |-). | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], 1.1.3..) | |
A reaction: This division can be mirrored in mathematics, where it is either to do with counting or theorising about things in the physical world, or following sets of rules from axioms. Language can discuss reality, or play word-games. |
9721 | A logical truth or tautology is a logical consequence of the empty set [Enderton] |
Full Idea: A is a logical truth (tautology) (|= A) iff it is a semantic consequence of the empty set of premises (φ |= A), that is, every interpretation makes A true. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], 1.3.4) | |
A reaction: So the final column of every line of the truth table will be T. |
9994 | A truth assignment to the components of a wff 'satisfy' it if the wff is then True [Enderton] |
Full Idea: A truth assignment 'satisfies' a formula, or set of formulae, if it evaluates as True when all of its components have been assigned truth values. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], 1.2) | |
A reaction: [very roughly what Enderton says!] The concept becomes most significant when a large set of wff's is pronounced 'satisfied' after a truth assignment leads to them all being true. |
9719 | A proof theory is 'sound' if its valid inferences entail semantic validity [Enderton] |
Full Idea: If every proof-theoretically valid inference is semantically valid (so that |- entails |=), the proof theory is said to be 'sound'. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], 1.1.7) |
9720 | A proof theory is 'complete' if semantically valid inferences entail proof-theoretic validity [Enderton] |
Full Idea: If every semantically valid inference is proof-theoretically valid (so that |= entails |-), the proof-theory is said to be 'complete'. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], 1.1.7) |
9995 | Proof in finite subsets is sufficient for proof in an infinite set [Enderton] |
Full Idea: If a wff is tautologically implied by a set of wff's, it is implied by a finite subset of them; and if every finite subset is satisfiable, then so is the whole set of wff's. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], 2.5) | |
A reaction: [Enderton's account is more symbolic] He adds that this also applies to models. It is a 'theorem' because it can be proved. It is a major theorem in logic, because it brings the infinite under control, and who doesn't want that? |
9996 | Expressions are 'decidable' if inclusion in them (or not) can be proved [Enderton] |
Full Idea: A set of expressions is 'decidable' iff there exists an effective procedure (qv) that, given some expression, will decide whether or not the expression is included in the set (i.e. doesn't contradict it). | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], 1.7) | |
A reaction: This is obviously a highly desirable feature for a really reliable system of expressions to possess. All finite sets are decidable, but some infinite sets are not. |
9997 | For a reasonable language, the set of valid wff's can always be enumerated [Enderton] |
Full Idea: The Enumerability Theorem says that for a reasonable language, the set of valid wff's can be effectively enumerated. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], 2.5) | |
A reaction: There are criteria for what makes a 'reasonable' language (probably specified to ensure enumerability!). Predicates and functions must be decidable, and the language must be finite. |
9723 | Sentences with 'if' are only conditionals if they can read as A-implies-B [Enderton] |
Full Idea: Not all sentences using 'if' are conditionals. Consider 'if you want a banana, there is one in the kitchen'. The rough test is that a conditional can be rewritten as 'that A implies that B'. | |
From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], 1.6.4) |
1556 | By nature people are close to one another, but culture drives them apart [Hippias] |
Full Idea: I regard you all as relatives - by nature, not by convention. By nature like is akin to like, but convention is a tyrant over humankind and often constrains people to act contrary to nature. | |
From: Hippias (fragments/reports [c.430 BCE]), quoted by Plato - Protagoras 337c8 |
6000 | The goal is rationality in the selection of things according to nature [Diogenes of Babylon, by Blank] |
Full Idea: Diogenes of Babylon defined the goal to be rationality in the selection and rejection of the things according to nature. | |
From: report of Diogenes (Bab) (fragments/reports [c.180 BCE]) by D.L. Blank - Diogenes of Babylon | |
A reaction: This captures the central Stoic idea quite nicely. 'Live according to nature', but this always meant 'live according to reason', because that is (as Aristotle had taught) the essence of our nature. This only makes sense if reason and nature coincide. |
5999 | The good is what is perfect by nature [Diogenes of Babylon, by Blank] |
Full Idea: Diogenes of Babylon defined the good as what is perfect by nature. | |
From: report of Diogenes (Bab) (fragments/reports [c.180 BCE]) by D.L. Blank - Diogenes of Babylon | |
A reaction: This might come close to G.E. Moore's Ideal Utilitarianism, but its dependence on the rather uneasy of concept of 'perfection' makes it questionable. Personally I find it appealing. I wish we had Diogenes' explanation. |
6001 | Justice is a disposition to distribute according to desert [Diogenes of Babylon, by Blank] |
Full Idea: Diogenes of Babylon defined justice as the disposition which distributes to everyone what he deserves. | |
From: report of Diogenes (Bab) (fragments/reports [c.180 BCE]) by D.L. Blank - Diogenes of Babylon | |
A reaction: The questions that arise would be 'what does a new-born baby deserve?', and 'what do animals deserve?', and 'does the lowest and worst of criminals deserve anything at all?' |