Questions tagged [deduction]

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11
votes
3answers
2k 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 ...
4
votes
3answers
2k views

What is the logical form of the definition of validity?

My text book gives the definition of validity as "An argument is valid IFF if the premises are true, then the conclusion must be true". Using a conditional elimination on the RHS of the IFF yields "An ...
10
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2answers
1k 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 ...
2
votes
6answers
292 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.
1
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2answers
143 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 ...
8
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5answers
4k views

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 ...
6
votes
1answer
9k views

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 ...
4
votes
2answers
111 views

help with deductive proof

∀x (Fx ∨ x=c), ¬Fb ∧ Gb |- ¬Fa → Ga So far I don't understand how to switch variables around to prove the result. I've got a subproof set up assuming "¬Fa" in order to derive "Ga". In that proof I ...
1
vote
2answers
492 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, ...
1
vote
0answers
107 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 ...
1
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2answers
2k views

How to get proof using proof editor and checker

How can I use Natural deduction proof editor and checker or The Logic Daemon to derive the given conclusion from the given premise: (∃x) ( Fx ∙ (y) (Fy → y = x) ) / (∃x) (y) (Fy ≡ y = x) It tells me ...
0
votes
3answers
227 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?