Deductive validity
An argument is deductively valid when if its premises are all true then its conclusion would have to be true
Deductive invalidity
An argument is deductively invalid when if all the premises were true the conclusion could still be false
Deductive soundness
An argument is deductively sound if it is valid and all of its premises are true
Deductive unsoundness
An unsound argument is a deductive argument that is invalid, has one or more false premises, or both.
Lexical ambiguity
Words or phrases in the sentence which have more than one meaning
Syntactic ambiguity
To do with whole sentences which are so arranged to have more than one meaning
Appeal to emotions
Rhetorical ploys which try to influence us by appealing to certain emotions
Trading on implication
Implying a statement without asserting it
Trading on equivocation
Exploiting the ambiguity or vagueness of a word or phrase
Affirming the…
Consequent
Denying the…
Antecedent
Deriving an ‘ought’ from ‘is’
When a prescriptive conclusion is drawn from a descriptive premise
Substantive fallacy
An argument which has as one of its premises a very general unjustified or false assumption
Ad hominem
Responding to an argument by attacking the person, or rejecting a particular claim because of dislike or disapproval for the person who made it
Ad hominem circumstantial
Rejecting or discounting someone’s arguments in favour of something on the grounds that they would benefit from our doing/believing it
To quoqe
Rejecting or discounting someone’s argument in favour of acting/not acting in a certain way on the grounds that they themselves do not act/ do act this way
Majority belief
The fallacy of concluding of concluding on the basis that most people believe something, P, then P must be true
Conflating morality and legality
This involves assuming that anything legal must be moral or vice versa
Illegitimate appeal to authority
Involves making an unjustified appeal to an alleged authority in order to support a claim
Perfectionist fallacy
Reject someone’s arguments in favour of a proposal to address a problem on the grounds that it won’t completely solve that problem
Post hoc ergo propter hoc
Mistakenly inferring that because Y occurred after X that X caused Y
Correlation for cause
Mistakenly taking that fact that one type of event usually or always happens in conjunction with another event to be sufficient to establish that one event causes the other
Weak analogy
Involves assuming that because one thing is similar to another in one respect, it similar to it in all relevant respects
False dilemma
Technique of limiting options on a particular issue to just two when in fact there are more options
Slippery slope
When an arguer wrongly assumes that to permit or forbid a certain course of action will inevitably lead to the occurrence of further related and undesirable events, without good reasons to suppose that the these events will follow
Begging the question
The truth of the conclusion is assumed by one or more of its premises and the truth of premises depend on the truth of the conclusion for their justification