Types Of Arguments Flashcards
Abduction
An abductive argument (which is often described as inference to the best explanation), is one that proceeds from an effect to argue for the most likely cause.
It usually draws on an inductive understanding of the world, but it distinguished from induction, partly because of the direction that your reasoning takes you - the direction of inference.
Abductions generally move in the opposite direction from inductions and deductions - they move from an effect (B), to a possible cause(B)
Examples: Sherlock Holmes notices the pavements outside wet, so after much consideration of all the alternatives, he concluded that this is because it has been raining.
The key features:
- the conclusion is never guaranteed, and an even better explanation is always possible.
- abductions attempt to go from an effect or observation to a possible reason or cause.
- abductions rely on our current beliefs concerning the way the world normally works.
An abduction cannot guarantee the truth of its conclusions, so like induction, it is not deductively valid.
It can on occasions however, masquerade as deduction - so one needs to be careful to recognise abduction, and not be fooled that is gives full support to its conclusion. The abductive inference is a logical fallacy - meaning that from a deductive point of view, it is a flawed piece of reasoning.
In a good abductive argument, the conclusion is only the best explanation given the available evidence - it is not guaranteed to be the case.
Key features of abduction
The key features:
- the conclusion is never guaranteed, and an even better explanation is always possible.
- abductions attempt to go from an effect or observation to a possible reason or cause.
- abductions rely on our current beliefs concerning the way the world normally works.
Example of abductive reasoning vs deductive reasoning
The rain making my roof wet:
Expressed as A-to-B deduction
Premise (A) If it is raining above my house, my roof will be wet.
Premise (A1) It is raining above my house
Conclusion (B) My roof will be wet
Here, the first premise is a hypothetical, and the second affirms that the antecedent is true, so the consequent necessarily follows.
However, if the reasoning was backward
P1 if it is raining above my house then my roof will be wet
P2 my roof is wet
C it is raining above my house
then the conclusion is not necessarily true, the reasoning would be wrong. Something else could have caused the roof to be wet - neighbour could have sprayed it with a hose etc.
This fails as a deductive argument as it does not show that it must have been raining. Just becuase A implies B, it doesn’t mean that B implies A. It is a logical error to think that B does imply A, known as affirming the consequent.
This fallacy of reasoning is abduction - going from the consequent to the antecedent
Deduction
If the premises are true, then the conclusion must also be true. If we accept the premises, then we are forced into accepting the conclusion as well - it is impossible for the reasons to be true, and the conclusion to be false.
Deductive arguments are also called deductively valid, or valid.
Deductive arguments preserve truth
Syllogism
A syllogism is a kind of logical argument that applies deductive reasoning to arrive at a conclusion based on two propositions that are asserted or assumed to be true.
They typically have a general claim, a more specific claim, and a conclusion.
P(1) All birds have feathers
P(2) My parrot, Kenny, is a bird
C Therefore Kenny has feathers
P1 All men are mortal
P2 Socrates is a man
C Socrates is immortal
Hypothetical claims in deductive arguments
P1 If a mushroom has brown gills, then is is safe to eat.
P2 This mushroom has brown gills
C Therefore, it is safe to eat.
In this deductive argument, the first premise is known as a hypothetical claim.
These claims have two parts - the ‘if’ part known as the antecedent (in this case ‘a mushroom has brown gills’, and the ‘then’ part (n this case ‘the mushroom is safe to eat’)
Hypothetical claims don’t tell us what is the case, but what would be the case if the antecedent is true.
Key features of a valid deductive
The conclusion must follow from the premises.
If the premises are true, then it is certain that the conclusion is also true.
All of the necessary information is in the premises, and no new information is gained in the conclusion.
Criticism of deductive arguments
This type of reasoning does not give us any new information - all the information that we get in the conclusion is already contained in the premises - the reasoning just draws out what might not be obvious at first sight.
Because of this, deductive arguments are not much use when it comes to discovering new truths.
Validity
Validity relates to the form of the argument.
An argument where if the premises are true, then the conclusion must also be true. The conclusion must follow on from the premises to be valid.
All proper deductive arguments are valid.
Example of an invalid argument:
P1 All bunnies are mammals
P2 Wilbur the cat is not a bunny
C Therefore Wilbur is not a mammal.
Soundness
Soundness relates to an arguments premises and it’s form.
Sound arguments are commonly referred to as proofs. A sound argument is also said to prove its conclusion.
To be sound, an argument must be valid (the conclusion follows from premises) and have true premises.
If the premises are not true, the argument is not sound, however, it could still be a valid argument if it has a valid form.
Induction
This involves generalising about how the world is and/or will be. They are based on observations of how the world is, and the truth of the conclusion is never guaranteed, even if the premises are true.
The two key types of induction are:
A - Generalising fro the past to the future. Example: observing that the number 343 bus has been late every day this week, so believing it will be late again today.
This one might be termed weak induction, as its only based on a few examples. A stronger claim might be based on a larger number of experiences.
B - Generalising from a restricted number of cases, to an unrestricted number (all cases). Example: observing that all life forms on earth are carbon based, so claiming that all life forms in the universe are carbon-based.
Induction can occur formally in science, but it also is something our minds do automatically for us.
The key features of induction
Even if the premises are true, the conclusion is never guaranteed to be true.
Inductions can come with different degrees of probability, depending on the strength of evidence.
Inductions attempt to go beyond the premises to make claims about how the world is, or will be.
Inductions move from cases / examples / effects in the past or present to conclusions about the present or future.
