# Questions tagged [logic]

For questions about logic, whether it concerns syllogistic logic, mathematical logic or the nature of logic itself.

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225 views

### Some questions on Graham Priest's remarks about Russell's solution of paradoxes

In his book Beyond the Limits of Thought while talking about Russell's solution of paradoxes Graham Priest writes (text made bold, footnotes and references omitted), Russell solved these problems ...
113 views

### How to define identity of intension?

In philosophy, there is much mention of the intension/extension distinction. Two properties can be extensionally equal but not intensionally equal. It is very easy to define when two properties are ...
168 views

### Why do we need Aristotle's theory of predication?

My question is about Aristotle's theory of predication. Why do we need it at all? I know it's intuitive to pick up something and say something about it like "S is P", but doesn't this lead us to ...
140 views

### How do you have to rate the probability of an existential claim?

If the prior probability of every universal hypothesis is zero how would you have to rate the probability of the statement that unicorns (at least one) exist? Probability of an event = number of ...
52 views

### Is double negation deconstruction applied to all branches of a truth tree?

If I am making a truth tree and already working on two branches when I come across a double negation (eg. ~~A), do I just decompose it to A right where it is, or do I add A to all branches? Hope I'm ...
177 views

### Why is Psychologism invalid according to Husserl?

I am having a difficult time understanding the critique of psychologism. From Dan Zahavi's book Husserl's Phenomonology: Logic (as well as, for instance, mathematics and formal ontology) is not ...
130 views

### compactness theorem failure in English

In this link they show how the compactness theorem fails in english: (first page with the starbucs example): https://ocw.mit.edu/courses/linguistics-and-philosophy/24-241-logic-i-fall-2005/readings/...
68 views

### Names for most popular taxonomies of informal fallacies?

Informal fallacies are not formal, so as might be expected, there exists no prevailing standard taxonomy. Various books on logic and logical fallacies organize fallacies differently, (see chapter ...
98 views

### What is the difference between Herbrand Logic and Relational Logic or Predicate Logic?

I am learning a course from Stanford University, and it introduces the notion of Herbrand Logic. However in Wikipedia I cannot find a definition specifically for "Herbrand Logic", only for Herbrand ...
370 views

### What is the difference between relational logic and predicate logic?

I am studying the Introduction to logic course from Stanford University and I begin learning about relational logic. However when I search on google for the terms there I end up often with results ...
143 views

### Formalize “Buffalo buffalo buffalo buffalo buffalo”

Source: p 145. Sweet Reason: A Field Guide to Modern Logic (2010 2 ed) by Henle, Garfield, Tymoczko. "Buffalo" sentences (pp. 73, 101, and 139) can be formalized if we establish two conventions. ...
51 views

### Can the material conditional be used in other situations?

Can the material conditional in classical logic (e.g. propositional logic or predicate logic like first-order logic) be used to reason about propositions that are not factual? E.g., using a ...
48 views

Given a flavor of nominalism which denies that simple sentences and existential quantifiers referring to mathematical objects are literally true (pretense theory, fictionalism, figuralism, etc.), ...
206 views

### If metaphysical grounding of beliefs is not necessary what is to logically compel one to believe anything?

'Grounding' is the notion that 'because of X, Y', X being the reason one can accept Y beyond pragmatic considerations. In this way, X and Y are analogous to cause and effect respectively. If it is ...
167 views

### Where can I find logical fallacies in action?

I'm looking for a website that gives logical fallacies in action. Not a video that explains logical fallacies, but a video, say a debate between two people where one of the debators uses a logical ...
53 views

### What are some alternatives to Mill's induction methods?

I have been taught that Mill's methods for identification of causes (agreement, difference, etc.) only apply when we can define our universe of possible causes very strictly (i.e., when we know all ...
82 views

### Does Every Logic Have the Potential for Violent Measurement?

Measurement, in the broad sense, involves useful abstractions and logical applicability that allow us to survey environmental data with extreme precision and prediction. The tools or instruments used ...
90 views

### Infinitary logic and algebra

After identification of equivalent formulas, is the algebra of formulas of a two-valued propositional calculus with infinitely long expressions a (free) sigma-complete Boolean algebra?
151 views

### What is a predicate according to Aristotle's Organon?

There is of course predicate as in predicate logic; but I'm asking about the notion in Aristotle's Organon. Consider the proposition: Socrates is a man. Man is a universal, Socrates is a ...
69 views

### Does anyone know of any essays on Adam's Thesis and Deontic Conditionals?

I'm curious if anyone knows of any essays which concerns how deontic conditionals fit with Adam's Thesis. (Adam's Thesis is the idea that the probability of an indicative conditional A > C is equal ...
1k views

### Testing the validity of syllogism argument

I came across a validation method for testing the validity of a syllogistic argument which seems quite easier to grasp: For example: To test the argument: no P is B some C is B Therefore, some ...
286 views

### Are numbers universal in Set Theory and nominalist in Category Theory?

The number 3, when considered as a universal, abstracts the property of 3'ness from all groups of 3 objects. One supposes that this universal, by conceptual neccessity of what is understood by the ...
253 views

### can we reason about logic?

People who study mathematical logic make arguments about logic itself. So it seems that people take for granted an "intuitive logic" (otherwise, how would they form arguments?). So the observation is ...
74 views

### Why can some arguments be proven only through Conditional or Indirect Proof?

For brevity, abbreviate as CP 'Conditional Proof', as DM 'Direct Method, and as IP 'Indirect Proof'. Source: p 445, A Concise Introduction to Logic (12 Ed, 2014) by Patrick Hurley Indirect proof ...
248 views

### to say that death is the end of life suggests that all living thing die?

i'am currently reading "thinking clearly about death" by jay Rosenberg and in 1.3 (chapter 1 part 3) he says to say that death is the end of life suggests that all living thing die it does not ...
111 views

### Did Wheeler's “It from Bit” allow inconsistencies to exist?

Physicist John Wheeler proposed a model of the universe based on "It from Bit" asserting that the world is fundamentally information. I've been told both that Wheeler's It from Bit is compatible with ...
69 views

### How and why Aristotelian essentialism is a problem for Quine?

I cannot understand how and why the Aristotelian essentialism is problematic for Quine. I have tried to read articles on the theme but probably I am not smart enough to understand them. Could you ...
110 views

### Where can I study this in more detail?

I am finding al-Farabi's Philosophy of Plato and Aristotle on pages 13-17, paragraphs 1-9, (pages 11-13 in the pdf file linked below), very interesting: http://traditionalhikma.com/wp-content/uploads/...
40 views

### What is a good history of logic book that covers all logic?

Including inductive, formal and mathematical. I find them separated a lot and I don't know if I have the ability to sit through all the Handbook of the History of Logic series.
131 views

### Is it there any trivialist model in physics (like in quantum mechanics)?

Trivialism is a system that proposes that literally every proposition is true and false at the same time blatantly breaking the principle of no contradiction and triggering the principle of explosion (...
45 views

### Logic-related note-taking question

I have been thinking about note taking from a logical perspective recently. It started when I realized that note-taking is basically a process of extracting "statements" or "arguments" from a piece of ...
89 views

### If logical propositions aren't tautologies (a la Wittgenstein), then what could they be?

This is a historical question about philosophical views. I believe I understand the claim made by Wittgenstein and others that logical propositions are tautologies. I'd like to know what other views ...
118 views

### Checking the validity of the logical conclusion gleaned from a heated conversation

I have two friends - call them John and Jane. I was recently privy to an argument concerning a book between John and Jane that went like this: John: This book did not make a single coherent, ...
88 views

### The illogical nature of want/motivation and its effects on free will

Are all the decisions and desires of humans made in order to stimulate pleasure centers and avoid pain? If so, could someone/thing which is unable to feel pleasure and pain, and only had the power of ...
88 views

### Lists and predicates on lists in classical first order logic

I have to express some basic Prolog code in classical first order logic (FOL). In Prolog i use lists, together with member/2 and append/3 a lot. Could you give me some tips for writing clauses like ...
84 views

### Trying to decide if the terms “proper education”, “real world education”, “successful life” are vague or ambiguous?

I feel that all three of these terms can have different meanings, but are they all vague as well? For example, proper education could mean a university education/college education/education in the ...
177 views

### De Morgan for Quantifiers Formal Proof: ∀∃-intro and -elim Questions

I have a problem reading existing question's answers. I've successfully encoded the proof of one of De Morgan's Laws, ¬∃x P(x) → ∀x ¬P(x), for Quantifiers formally via cubicaltt type-checker via Curry-...
156 views

### Semantic expressiveness of modal logic

I am wondering how much of the semantic of basic philosophical questions can be expressed by formal arguments in modal logic. Here is one argument I formalised myself: P1 ◇ ∀a, ∃x // GNB(x, a) ∧ ...
68 views

### What irreducible functions constitute thinking?

Because all new knowledge, to be not illogical, must obey logic i.e. every thinking step must be consistent with rules of logic; so can we write an effective procedure/algorithm which may be followed ...
32 views

### Can the conclusion of an inductive argument be that there is only one exception to the list of evidentiary claims?

Can this be an example of an inductive argument? Premise 1: Country A rejected idea Z. Premise 2: Country B rejected idea Z. Premise 3: Country C rejected idea Z. Premise 4: Country D rejected ...
28 views

### What criteria does Frank Jackson give in order to assert the negation of a conditional?

In Frank Jackson's paper, On Assertion and Indicative Conditionals he gives a criteria for when one should assert a conditional (material conditional). This criteria is given in terms of conditional ...
34 views

### Recommendation: Second Order Logic textbook

I'm looking into Universalist Realism, Nominalism, Trope theory and the application of Second Order logic to each of them, however I have little/no experience with Second Order logic. Please let me ...
84 views

### Proof from tree to steps

I'm able to get the proof in a tree form (it's invalid). Is there a method where I can transform it to steps method indicating the rules of inference and replacement?
204 views

### What is the difference between ampliative, abductive and inductive arguments?

I know all these arguments are kind of the same but what is the border dividing them?
99 views

### What is an example of a predictive conditional?

Can someone explain to me with an example what a predictive conditional is? Does this type of conditional have necessary and sufficient conditions?
83 views

### syllogism, truth-functional, or neither?

I dreamed that John F. Kennedy was born in 1917, and everything I dream is true. Therefore, Kennedy was born in 1917. All horses are animals. Therefore, all heads of horses are heads of animals. If '...
74 views

### How should one reconcile predicate functor logic with Quine's own ontological theory?

Quine proposed that "to be is to be the value of a variable". However, he also devised predicate functor logic (PFL), which effectively gives a recipe for eliminating bounded variables. How should ...
119 views

### Understanding Lewis Carroll's argument on Modus Ponens

I read in an answer somewhere on this site that Modus Ponens involves an infinite regress. Upon reading Lewis Carroll's Achilles and the tortoise, I fail to see how. This is the excerpt from ...