Philosophy Stack Exchange
Philosophy Stack Exchange

Questions tagged [deduction]

126 questions
42
votes
11 answers

Fallacy by Sherlock Holmes 'Eliminate the impossible, and what remains must be the truth'

In The Sign of Four, Holmes asks Watson: "How often have I said to you that when you have eliminated the impossible, whatever remains, however improbable, must be the truth?" This may be valid in principle, but it certainly carries the risk of a…
Mogli
  • 447
  • 1
  • 4
  • 7
18
votes
6 answers

If math is so deductive, why is it so hard to discover new math?

Some considerations: The conclusions of much latter/new math may be said to be already existent within the premises of current math The importance of deduction changes depending on if math is said to be invented or discovered Some parts of math…
Xeon
  • 441
  • 2
  • 7
11
votes
2 answers

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 reasoning, surely, forming 'general' opinions or…
Selena Carlos
  • 451
  • 3
  • 10
11
votes
3 answers

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 believe that the usage of "clearly" makes this…
Ben
  • 165
  • 5
11
votes
2 answers

What's the relevance of falsifiability in regards to logical arguments?

Is it reasonable to classify logical propositions that rely on deduction and are non-falsifiable as being inherently not worthy pursuing or does this just applies to inductive reasoning?
Trinidad
  • 208
  • 2
  • 8
7
votes
6 answers

Are "If P then Q" and "Q only if P" equivalent?

My textbook says "If P then Q" and "Q only if P" are logically equivalent, but consider this: "If it's green, it's poisonous." "It's poisonous only if it's green." Now say there's a purple poisonous frog. The first statement is true and the second…
Vibhanshu Bhardwaj
  • 81
  • 1
  • 3
7
votes
1 answer

The difference between argument, inference, deduction and proof?

I am trying to distinguish argument, inference, deduction and proof. First, let's look at the distinction between argument and inference (if there is one). This online source states: An argument is a set of two or more propositions related to each…
EthanAlvaree
  • 809
  • 1
  • 8
  • 16
6
votes
5 answers

What is the nature of "validity" in deduction when dealing with conclusions unrelated to premises?

I studying graduate math (not very far into it), and I realized that some of the higher-level math texts I would like to read are hard to understand without a strong basis in logic. Now I've taken elementary courses (like general college first year)…
Zduff
  • 171
  • 4
5
votes
6 answers

What is the relationship between algorithms and logic?

Is an algorithm (cooking a dish, Grover's/Shor algorithm, etc.) a form of deductive reasoning or inductive reasoning, and if not what exactly is the relationship between an alogorithm and logic?
quanity
  • 958
  • 3
  • 15
5
votes
1 answer

Why does Gensler's Star Test not work on some syllogisms?

All teachers are intelligent. All teachers are well-paid. From the Star Test, we can deduce that the argument must be invalid with whatever conclusion (according to the classical syllogism figures), because All T* is I. All T* is W. Here T is…
user47471
5
votes
1 answer

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 attempt: Predicates: Tx: x is a turtle Sxy: x sees y…
Rob
  • 153
  • 3
5
votes
1 answer

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 the principle of nature's uniformity: The principle…
MadRabbit
  • 153
  • 4
5
votes
5 answers

Proof that deduction is valid in all possible realities?

I was wondering, how can we know that deduction is a valid way to argue for something in all possible realities? How do we know that, in some alternative universe, something is not both ~P and P? How can we know it is valid in our reality? It…
user15247
5
votes
2 answers

What is this technique to gain proof called?

I just found out that I always missused the term deduction. I always thought that deduction meant gaining a proof by showing that all the other possible answers are wrong. But deduction is actually something like this: All men are green John is a…
Hans Wassink
  • 153
  • 4
5
votes
2 answers

Malthus's argument on population - Test 1, Q14, by Mark Shepherd

I took a practice test for a law exam and am having difficulty with understanding the logic behind a question. Apologies for the length, but I included the whole question and details for completeness. Until the middle of the eighteenth century, the…
user8572
1
2 3
…
8 9