The Student Learning Centre
Building a Logical Argument
Other handouts:
 Analysing an Essay Question
 Structuring an Essay I
 Structuring an Essay II
What is an ‘argument’?
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An argument is a claim supported by related premises;
Logic is coherent reasoning.
Premises are statements offered in support of an argument or claim;
A good, logical, argument is therefore a claim that is coherently supported by premises
(‘evidence’). The claim may be valid, and the premises may be valid, but a sound or weak
argument rests on the match between the overall claim and its premises. A coherent match makes
a logical argument; an incoherent match is called a fallacy.
In academic writing, scholars and professionals advance arguments in logical ways, so that
claims are carefully supported by clear and persuasive ‘evidence’. There are two argument
structures:
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A deductive argument is one that rests heavily on its premises and allows these to lead
to the conclusion (a deduction). This does not mean that the deductive argument is
necessarily or automatically logical – you can make a strong or weak deductive argument.
It just means that the evidence is assumed to ‘speak for itself’. The validity of the
deductive argument therefore rests very strongly on the validity of the premises/evidence.
Example of deductive arguments:
Valid deductive argument
All men are mortal
Socrates is a man.
Therefore, Socrates is mortal.
Invalid deductive argument
All men are mortal.
Socrates is mortal.
Therefore, Socrates is a man.
In valid arguments, accurate premises always guarantee an accurate conclusion. However
invalid arguments can have any combination of accuracy and inaccuracy in their premises and
conclusions. Deductive arguments are either valid or invalid. They are often made in
scientific or statistic fields that require solid data. (However, the ultimate ‘truth’ of any
argument is still subject to speculation and interpretation, in the final analysis).
1. An inductive argument is not based on its premises, but is a contention or statement of
probability. An inductive argument is not based on the accuracy of its premises but on its
persuasive element. Therefore, inductive arguments are weak or strong – they are
assessable as being relatively valid or invalid.
Examples of inductive arguments:
Sound inductive argument.
Many people who smoke get lung cancer.
Most lung cancer patients have been smokers.
Smoking is dangerous.
Weak inductive argument
Many people who smoke get lung
cancer.
Not all lung cancer patients die.
Smoking is dangerous.
The sound inductive argument does not rely totally on the premises to conclude that there is
likely to be a connection between smoking and lung cancer. The claim that smoking is dangerous
is supported by logical evidence that does not need to be conclusive. The weak argument is
ineffective because the premises do not match the conclusion, making it less convincing.
A good essay plan (see Essay Writing I handout) will ensure that your argument, whether
deductive or inductive, is a sound one, in which the thesis is supported by valid and relevant
premises. The important thing is that they must all be connected and relevant to each other.
Fallacies
A fallacy is an argument that is unsound because it is structurally flawed in its logic or reasoning.
Some common fallacies include the following:
Begging the Question
The conclusion is really one of the premises in disguise. This leads to the reader ‘going round in
circles’ because the argument does not lead anywhere.
Example:
‘We demonstrate to the hypochondriacs that they are no different from anybody else because
everybody gets sick sometimes.’
The point about hypochondriacs is that the sufferer is very afraid of being sick. The premise that
people get sick) is ‘circular logic’ and does not advance the argument in any useful direction (ie.
the conclusion and the premise for the conclusion are the same thing).
Ad Hominem argument
This is an argument directed against a person, on the basis that a discredited person cannot stand
for anything valid. Adversarial systems of government often deploy this as a means of gaining
credibility for themselves by default.
Example:
‘Joe Smith was reported to have left his hotel without paying his bill. Why would we think that
his audit of the Treasury Department is accurate?’
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False Dilemma
A ‘dilemma’ refers to a difficult choice. A false dilemma offers a choice on the misleading
premise that only one of them can be true or valid. This can be done unknowingly or
deliberately, in the sense of an argument this still results in a fallacy – a flawed piece of logic.
Some false dilemmas are very obvious; others are more subtle. Some lawyers present false
dilemmas to juries, with the intention of weighting the verdict.
Example:
‘Either Ms Jones is a very confused senior manager (which her rapid ascendance in Parsons and
Green does not imply), or she is very clever at concealing her true intentions.”
These are not the only choices, but the audience is being directed to choose between two
statements, either of which may be true or false.
Irrelevance
This is when the premises of an argument actually bear no relation to the conclusion.
Example:
‘Fruit is good for you because it is natural.’
Many substances from nature are highly toxic to humans for a variety of reasons. The premise is
accurate (fruit is natural) but irrelevant to the argument that it is good for you.
Generalisation
Because something may be true in some cases and contexts, does not mean it is generally true.
Academic writing should avoid unsupported generalisations, unless there is reasonable evidence
of its wide acceptance. Stereotypes are constructed this way. Generalisations are frequently
based on a particular view disguised as an overall truth.
Example:
Australians aspire to owning a home on a quarter-acre block, and to enjoying a beer on the
verandah on a hot afternoon.
This is based on a specific image of ‘the Australian’ as being a white, working class male person,
living in the suburbs at a time when quarter-acre blocks for single dwellings were affordable.
Beer-drinking is a part of this image. It does not represent Australians as a diverse population.
Appeal to authority
This argument draws on the status of an expert to lend credibility. It is certainly common
practice in academic writing to back up key points with the work of established scholars.
However, an argument is not valid purely because of the arguer’s credentials.
Example:
If it’s good enough for the leader of the free world, it is surely good enough for you.
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Popular Appeal
This fallacy contends that if something is widely popular, or widely believed, then that attests to
its validity. It is a kind of ‘common sense’ argument (This is similar to the appeal to authority.)
Whilst popular opinion cannot be ignored, an argument is based on its demonstrated logic, not on
its popularity. Like the generalisation and appeal to authority, the claim is not sufficiently
supported with supporting evidence or premise.
Example:
This is an idea endorsed by the ‘lunatic fringe’ of our society. Very few ordinary people would
entertain this kind of thing.
The contention that most ‘ordinary’ people don’t like something does not have a bearing on its
validity or potential value.
Tips for building a logical argument:
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Choose a claim that is supportable by carefully-linked evidence
Be clear whether your thesis is based on a likelihood or a certainty, and word it
accordingly.
Choose and apply credible research sources
Don’t bluff, exaggerate, guess or make unsupported claims
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