What kinds of formal logic have applications in law?
<p>There are different kinds of formal logic: propositional, first order, second order, modal, fuzzy, .... What kinds of formal logic have applications in law? Thanks.</p>

<blockquote>
<p>The Life of the Law Has Not Been Logic; It Has Been Experience.</p>
</blockquote>
<p>-- Oliver Wendell Holmes, Jr.</p>
<p>Basically none.</p>

<blockquote>
<p>The common law is tolerant of much illogicality, especially on the surface; but no system of law can be workable if it has not got logic at the root of it.</p>
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<p>(Lord Devlin, Hedley Byrne &amp; Co., Ltd v Heller &amp; Partners [1964] AC 465, 516)</p>
<p>To think like a lawyer, you need to use <a href="https://www.deakin.edu.au/__data/assets/pdf_file/0005/728105/du-legalreason.pdf" rel="nofollow noreferrer">three</a> types of logical reasoning:</p>
<ul>
<li><a href="https://en.wikipedia.org/wiki/Argument_from_analogy" rel="nofollow noreferrer">reasoning by analogy</a>,</li>
<li><a href="https://en.wikipedia.org/wiki/Inductive_reasoning" rel="nofollow noreferrer">inductive reasoning</a>, and</li>
<li><a href="https://en.wikipedia.org/wiki/Deductive_reasoning" rel="nofollow noreferrer">deductive reasoning</a></li>
</ul>
<p>However, the standard required is not rigorous logical proof, it is reasonableness. That is, on the evidence provided, is it open to a reasonable person to draw the conclusions that the decision maker made.</p>

theory-of-law