Key Terms Flashcards
Under what circumstances is Y a consequence of sentences ‘X1,…,Xn’
Iff. There is no case where ‘X1,..Xn’ are all true and Y false
-> ‘X1,…,Xn’ entail Y
Valid
Off. There is no case where all the premises are true and the conclusion false
Invalid
If there is some case where the premises are true and the conclusion false
Nomologically Valid
If an argument has no counter examples that don’t violate the laws of nature
Conceptually valid
If there are no counter examples that don’t violate the conceptual connections between words
Formally valid
Either a is an F or a G
a isn’t an F
Therefore: a is a G
Is it possible for a valid argument to have a false conclusion
Yes, the premises and conclusion may both be false
Eg. Oranges are fruits or animals
Oranges aren’t fruit
Therefore: Oranges are animals
What is important is that if the premises were to be true would the conclusion also have to be true
Hypothetical rather than actual truth
An argument is sound if and only if …
It is both valid and it’s premises are true
Ampliative Arguments
An argument where the conclusion goes beyond the premises
Moves from the observed cases to generalisations
Eg. All observed F’s are G’s
All F’s are G’s
Joint possibility
Iff. There is a case where all the sentences are true together
Eg. Janes only brother is shorter than her
Janes only brother is younger than her
Jointly Impossible
If the sentences are not all true together
Eg, Joe’s only sister is younger than him
Joe’s only sister is older than him
Contingent
A sentence which under different circumstances can be true or false
Necessary truth
A sentence that is true in every case
Necessary falsehood
A sentence that is false in every case
Necessary equivalent
If two sentences have the same truth value in every case
