# Questions tagged [deduction]

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### (p->q) v (q->p) with Natural Deduction

Well, indeed I have the answer to this exercise but I don't understand some steps. From 6 to 17 are OK for me but from 2 to 5 and then when step 5 is again called in step 10 is something I don't get ...
495 views

### Why is this deductive reasoning incorrect?

All goats have a beard. Karl Marx had a beard. So, Karl Marx is a goat. Here, first premise = "All goats have a beard" second premise = "Karl Marx had a beard" conclusion = "Karl Marx was a goat" ...
57 views

### Thoughts on Open Logic Project?

I'm currently thinking about starting to expand my knowledge of logic beyond what I retain from my previous study of logic by making use of the materials available through: OpenLogicProject (https://...
38 views

### Clarifications on 1) Modus Ponens, 2) Modus Tollens, 3) Inductive, 4) Incomplete based on examples

My second lecture on Hypothetico-Deductive methods (based on Popper's falsification theory). In the class, we were given the following examples. We had to classify which examples belong to 1) Modus ...
162 views

### Does the Law Of Excluded Middle Apply to the Principle Of Identity and Non Contradiction? [closed]

This argument will seem confusing, precisely because it observes the laws of identity being subject to equivocation. If this is kept in mind, the following should make more sense and explain why the ...
44 views

### Reasoning for Inductive inference?

Just out of curiosity, if I should replace the deductive inference related questions to inductive inference, then which are true? Inductive inferences rearrange current knowledge in such a way that ...
41 views

### Reasoning for deductive inference?

I got a quiz today in my classroom. I need to say True or False to the following: Deductive inferences are typically based on unfounded assumptions. For the valid deductive inference, the conclusion ...
45 views

### What are some key differences between an argument in logic and a theory in mathematics?

Both are composed from rules and assumptions which enable us to deduce other inevitable truths that results from these rules and assumptions, right?
65 views

### Are there rules for the following in the Open Logic Project's proof checker?

I'm using http://proofs.openlogicproject.org/ but can't find out what the translation of the rules are. I'm new at this, so when I try to make proofs, I know what I want the justification to be (which ...
62 views

### How to solve this natural deduction problem?

This one is driving me crazy. I don't understand most keys for de morgan, modus ponens, etc, so please abbreviate if possible? EX: DM, MP, SIMP, HS, Conj, Imp (material Implication). Thank you anybody ...
203 views

### Confusion between deductive and inductive reasoning definitions

The following arguments is always given as a classic example to deductive reasoning: All men are mortal. (First premise) Socrates is a man. (Second premise) Therefore, Socrates is mortal. ...
37 views

### Quick question on discharging assumptions

Could someone explain conceptually what the consequences are of assumptions NOT being discharged in a natural deduction ? Suppose the objective is to establish a claim of the form : 'If A,then B.' ...
168 views

### What is a natural deduction proof from ~(A↔B) to ~(A→B)?

It feels intuitively correct, but I cannot work out how to prove it. I would appreciate any help.
238 views

### What is the difference between the resolution rule and the elimination in natural deduction?

I understand that elimination is: p v q ¬q then p and resolution is: q1 v q2 v q3...qn ¬q1 v q2 v q3...qn then q2 v q3...qn I see no difference, but my teacher is telling us don't use the ...
157 views

### Tacit inferences?

Does anyone give a useful account of tacit inferences? I am interested in the psychological notion of inference here, and do not in the context focus upon the logical notions of validity and soundness....
415 views

### If turtles see everything, and nothing seen can see, does it follow that non-turtles exist?

Consider the following argument: Turtles see everything. Seeing is asymmetric (for the sake of argument). Therefore, something is not a turtle. I have problems symbolizing these statements. My ...
110 views

### Is deduction based on induction?

I'm wondering if deduction is in the end based on induction. The problem of induction discovered by the Scottish philosopher David Hume is quite well known. On the other hand, it's commonly supported ...
216 views

### Can all inductive arguments be written as deductive arguments?

Whenever I see inductive arguments being used, it seems as though they can be redone by simply making certain assumptions and rephrasing the argument as a deduction from those assumptions. For ...
72 views

### ~(~P&Q) & ~(P&Q) : Prove ~Q

This must be proved using only negation, double neg.Intro, double negation Elimination, indirect proof, conj.Intro, and conj.Elim.
774 views

### How to get proof using proof editor and checker

How can I use http://proofs.openlogicproject.org/ or http://logic.tamu.edu/daemon.html to derive the given conclusion from the given premise: (∃x) ( Fx ∙ (y) (Fy → y = x) ) / (∃x) (y) (Fy ≡ y =...
169 views

### Does Hume reject the possibility of is-ought syllogisms?

Suppose the following syllogism: It is impossible for anyone to get X without him/her doing Y. It is possible to get X (by doing Y). I want to get X. Therefore I ought to do Y. There is, very likely,...
617 views

### How do I operate with philosophers if I reject deductive reasoning?

Deductive reasoning is the one that takes premises for granted. I never do it. Therefore I never do deductive reasoning. Well, enough jokes. It is safe to assume that deductive reasoning never should ...
154 views

### Is there a single definition of truth?

Is there a single definition of truth in philosophy? Seeing multiple definitions has inclined me to believe that there is no proper definition of philosophy that everyone can agree on.
1k views

### Inductive and deductive arguments and mathematical induction

I started reading Paul Teller's A Modern Formal Logic Primer. In the first chapter, the book presents the inductive and deductive arguments with the following examples: The inductive argument: ...
397 views

### Justification of deductive reasoning

Is a justification of deductive reasoning possible? If so, please tell me how because whenever I try to form a justification of deductive reasoning I end up committing the fallacy of circularity.
135 views

### How can I prove ⊢(∀x)(Fx V ~Fx) with natural deduction?

⊢(∀x)(Fx V ~Fx) How can I prove this with natural deduction?
241 views

### Natural deduction proof help!

I've gone through about 40 natural deduction proofs in the past couple days, and mostly they are no problem. For some reason, I've been stuck on 1 tedious problem for an entire day. I just can't seem ...
812 views

### Does an implied premise mean a formal fallacy if used in deduction?

Let's just say we have an implied premise: 2.a Socrates is a philosopher (implied premise), but not explicit Then is the following a formal fallacy? Socrates is a man. All men are mortal. ...
594 views

### Deriving “(p.q) v (p.r) from ”p.(q v r)"?

I am new to logic. and here are my tryouts for deriving deriving "(p.q) v (p.r) from "p.(q v r)", and further I want to show that ”p.(q V r)” is equivalent to ”(p.q) V (p.r)”, by using natural ...
794 views

### Is there a deduction analog to the problem of induction?

Aren't deductive and inductive reasoning equally unjustified? So, inductive reasoning is going from specifics to general, whilst deductive reasoning is going from general to specific. But in deductive ...
275 views

### In fitch, S → (R ∨ P), P → (¬R → Q) ∴ S → (Q ∨ R)

Construct a proof for the argument: S → (R ∨ P), P → (¬R → Q) ∴ S → (Q ∨ R) I have gotten to the point in the illustration, but I am unable to figure out where to go from here. I get tricked up on ...
248 views

### Predicate logic proofs - how to split a disjunction bound by two quantifiers

I need to complete the following proof using only primitive rules (the introduction and elimination rules for each connective and quantifier). (∃x)(∀y)(Py ∨ Qx) ⊢ (∀y)Py ∨ (∃x)Qx I've only been able ...
83 views

### Is this a valid argument (using probability and uncertainties)?

If A, then B (probability of 0.6 that this is true) If B, then C (probability of 0.6 that this is true) A, Therefore C. I'm not sure whether C is probably true if A is true, or if the probability ...
637 views

### Why can't uniformity of nature (in principle) be proven deductively?

I've been reading about the problem of induction and I have trouble understanding the argument for nature's uniformity being impossible to prove deductively. Stanford Encyclopedia of Philosophy on ...
1k views

### Are “if smoke then fire” arguments deductive or inductive?

I'm new to philosophy and have a question regarding deductive vs. inductive reasoning: I'm told that "John ate a strange plant in the forest and got sick. Clearly, the plant made John sick." I ...
212 views

### Logic question regarding a logical truth

Is the following logically true? ∃x[Cube(x) →∀yCube(y)] I think that it is logically true. When translated into truth functional form we have: A→B. A truth table shows that it is not a tautology but ...
311 views

### Based on evolution, do we arrive at deductive principles inductively?

If our knowledge of deductive principles is a result of evolution... doesn't this mean that we arrive at deductive principles inductively? Assuming deductive principles are beneficial for survival, ...
157 views

### What are the rules for a zero-premise derivation involving disjunctions?

I'm having trouble with the following zero-premise deduction that involves two disjunctions: The solution seems simple, but I'm unsure of how to proceed with the two disjunctions. If it were just ...
512 views

### Is this an inductive or a deductive argument?

Two flowers of the same cultivar were planted in adjacent plots . The first was fertilized with Miracle-Gro and it flourished (2); The second was not and it din't(3) . Therefore , Miracle-Gro ...
195 views

### Quick logic deduction question

I have to provide a natural deduction derivation for: ¬∀xFx ⊢ ∃x¬Fx That´s what I got so far: 1.¬∀xFx 2.‖ ¬∃x¬Fx (Indirect proof hypothesis) 3.‖‖ ¬¬Fy (Indirect proof hypothesis 2) 4.‖‖ Fy (...
492 views

### Proof for the Rule of Absorption in Propositional Logic?

I know there is a "formal proof" for the "rule of absorption" that employs the "law of excluded middle". It is presented in Wikipedia (and I think it is Russell's): https://en.wikipedia.org/wiki/...
213 views

### Is this inductive or deductive?

The fact that we know we have a great great grandfather. Is the reasoning we use for this inductive or deductive?
433 views

### Implication Introduction formulated as a theorem?

While making a list of the rules of inference for my math students, I came across this list on Wikipedia: I noticed a pattern: for every introduction rule, there seems to be an elimination rule, and ...
154 views

### Is logic based on uncertainty the fundamental logic?

Most formal logics are based on certainty, but certainty is only one probability among others, so a logic based on uncertainty and probability should be considered as the fundamental logic from which ...
299 views

### How can one intuit that P → Q ≡ ¬P ∨ (P ∧ Q)?

I have not succeeded in intuiting P → Q ≡ ¬P ∨ Q in the sense of imagining how one would conjecture or divine the equivalence without any "foreknowledge" of ¬P ∨ Q to invoke formal proofs or truth ...
320 views

### Logical analysis of “Free will and god(s)” argument

Please evaluate the following argument strictly for formal logical validity. I am NOT interested in debating the content or in philosophical perspectives on the content. However, I AM interested in ...
904 views

### ⊢ ((AvB) -> C) -> (A -> C) using simple derivation rules

My thought process: - This derivation has no premises. - The desired conclusion is a conditional, therefore assume the antecedent and derive the conditional. What I have so far: 1 1) (AvB) -&...
134 views

### How to prove 1. ~(KvF) 2. ~F=>(KvC) 3. (GVC)=>~H / ~(KvH) using natural deduction

I need help with this question using the first 13 rules of inference. Here is what I have so far: ~(KvF) ~F=>(KvC) (GVC)=>~H / ~(KvH) ~Kv~F DM 1 ~Fv~K Com 5