Commercial Law
4 August 2026
Six Logical Fallacies That Weaken Legal Arguments
By Christopher N. Rosana
Logical fallacies weaken legal arguments because they replace the required chain from rule and evidence to conclusion with a shortcut. The remedy is not to make every submission academic. It is to identify the proposition that must be proved, the legal source that governs it, the facts capable of supporting it and the alternative explanation that must be answered. A court may reject a fallacious argument even where its conclusion could otherwise have been attractive. Sound advocacy therefore tests reasoning as carefully as it checks citations.
Ad hominem: attacking the person instead of the proposition
An ad hominem argument attacks counsel, a witness or a party rather than the legal or factual point. Saying that an opponent is inexperienced, evasive or commercially powerful does not answer a contractual clause, an evidential gap or a statutory requirement. Personal criticism can be relevant only where character, credibility, authority or conduct is genuinely in issue and the procedural basis for raising it exists.
Replace the label with the precise defect. Rather than saying a submission is dishonest, identify the document it omits, the authority it misstates or the factual inference it cannot support. This preserves professional tone and gives the court a proposition it can decide.
Straw man: answering a weaker case than the one pleaded
A straw man recasts the opponent’s position into an easier version and defeats that version instead. It may appear when a party answers a broad commercial complaint rather than the actual pleaded breach, or responds to a general principle while ignoring a specific statutory exception. It wastes space and risks conceding the real point by silence.
State the opposing proposition fairly before answering it. Identify its legal source, the facts it depends on and the remedy it supports. Then explain why the source does not apply, why the required fact is absent or why the proposed consequence does not follow. Fair framing is not concession; it is the beginning of a persuasive response.
False dilemma: treating two options as the only options
A false dilemma presents a choice as all-or-nothing where law or facts allow a third route. Common examples include saying the court must either enforce a contract exactly as claimed or deny all relief, or that a witness must be wholly believed or wholly rejected. Remedies may be partial, alternative or discretionary; evidence may establish one fact without proving every allegation.
Test the available legal outcomes. Ask whether the court can grant a lesser remedy, make a limited finding, sever a provision, order an account, allow amendment, or resolve one issue without deciding another. The answer may still favour the client, but the argument becomes stronger when it acknowledges the court’s actual choices.
Circular reasoning and bare assertion
Circular reasoning assumes what it needs to prove: the defendant acted unlawfully because the conduct was unlawful; the notice was invalid because it was ineffective. Bare assertion has the same practical weakness when it declares a conclusion without its supporting steps. Neither tells the court why the legal test has been satisfied.
Break the conclusion into elements. If the issue is validity of notice, identify the source of the requirement, the form or timing required, the evidence of what was done and the consequence of any defect. If an inference is required, state it openly and explain why the underlying facts justify it. A conclusion earns force from its reasoning, not its repetition.
Post hoc and unsupported causation
Events occurring in sequence do not necessarily prove causation. A loss that follows a breach may have another cause; a policy change followed by a commercial result may not have produced it. In litigation, causation often depends on contractual allocation of risk, intervening acts, expert evidence, foreseeability and proof of loss. Timing alone is rarely enough.
Identify the causal proposition precisely. What conduct is said to have caused which loss, through what mechanism, and on what evidence? Then test competing explanations and the claimant’s duty to mitigate where relevant. This analysis is especially important in damages claims, professional negligence and disputes involving complex commercial records.
Appeal to consequence or popularity
An argument may say that a conclusion must be right because another outcome would be commercially inconvenient, unpopular or morally unattractive. Consequences can matter where the statute, contract or discretion makes them relevant. They cannot replace the governing rule. Similarly, common industry practice may help interpret a term or establish a factual context, but it does not automatically displace an express obligation.
Use consequences in their proper place. First establish the legal route to relief. Then explain the practical effect where it bears on interpretation, proportionality, discretion or remedy. This order prevents policy preference from masquerading as legal entitlement.
Repair the argument before filing.
For every important conclusion, ask: what exactly must be proved; what authority creates the test; which evidence supports each element; what is the strongest contrary point; and what order follows? If the argument cannot answer those questions, refine it before it reaches the court. The Court of Appeal has stressed that parties are bound by their pleadings, so the analysis must remain tied to the case actually presented. This is general information, not advice on a particular proceeding.
Another common error is overgeneralisation. A party may take one disputed incident, one clause or one witness answer and use it to establish a much broader proposition. Test the scope of every conclusion. Does the evidence support this transaction, this period, this person and this remedy, or is the argument assuming more than the record can bear? Narrow arguments are often more credible and more useful.
Arguments from authority also require care. Citing a judgment because it contains favourable language is not enough. Identify the legal issue actually decided, the court that decided it, the material facts and whether later authority or legislation affects it. A quotation from a different context may be persuasive, but it should not be presented as controlling law without justification.
Quantification can conceal its own fallacy. A large number, percentage or comparison may sound decisive without a reliable denominator, sample or causal link. Ask what the number measures, who was included or excluded, how the figure was calculated and whether a different comparison changes the conclusion. Statistical and causal errors require separate attention because apparent precision can make an unsupported inference seem inevitable.
Use an adversarial read before filing. Ask a colleague or the drafting lawyer to identify the strongest answer to each issue, then revise the argument to meet it. This process does not weaken the client’s position; it prevents the submission from resting on an untested shortcut and improves the clarity of the final request for relief.
A disciplined argument also separates legal relevance from emotional force. A fact may be upsetting, commercially serious or morally unattractive yet still not establish the element required for the remedy sought. State why the fact matters under the governing rule. Conversely, do not dismiss a difficult fact merely because it is inconvenient; explain whether it is immaterial, unproved, outweighed or legally answered.
The final test is traceability. A reader should be able to trace each conclusion backwards to a legal test and a factual source, and forward to a practical consequence or order. That trace makes it easier to find a missing premise, an overstatement or a fallacy before the opponent or court does.
That method also makes collaboration safer: a supervising advocate can test the rule, factual premise and proposed consequence without guessing what the drafter assumed. It is a practical quality-control step for every important written argument.
It also gives the client a transparent explanation of why the position is sustainable, qualified or vulnerable before the matter reaches court. fully.
Part 11 of 24 in this series.