Constructing a Deductive Argument
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Constructing a deductive argument means choosing the conclusion first, selecting a valid form to carry it, drafting the premises that form requires, then stress-testing each before stating it.
Target conclusion: this bridge was not inspected last year. Choose a vehicle. Denying the consequent will carry it, so the form needs a conditional whose consequent can be denied. Draft premise one: if the bridge was inspected last year, an inspection report was filed with the county. Draft premise two: no inspection report for this bridge is on file with the county. Now stress-test. Premise one holds if filing is mandatory and reliably done, so the argument depends on that and it should be checked rather than assumed. Premise two rests on a records search, which is checkable. Now check the twin and dodge it. Affirming the consequent would run from a report being on file to an inspection having happened, which is invalid — and that is not the direction here. State it in standard form and symbolise: I horseshoe R, tilde R, therefore tilde I. The conclusion is modest, and that is the point. It claims only what the two premises will carry.
A valid form guarantees that true premises would deliver the conclusion, and nothing about whether they are true. An argument built form-first and never stress-tested is a well-engineered container for whatever was put in it.
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