If a witness refuses to answer &#39;Has the defendant done this before?&#39;, then why can the jury appeal to ignorance?
<p><sub>Source: p 186, <em>The Art of the Advocate</em> (1993) by <a href="http://www.independent.co.uk/news/people/obituary-richard-du-cann-1375068.html" rel="nofollow noreferrer">Richard Du Cann QC</a> (called to the Bar of England and Wales).</sub></p>

<blockquote>
  <p>  Until then great attention will be paid to any question asked 
  by the jury on the nod and wink principle referred to. Counsel 
  will do anything they can to answer, or to explain why they 
  cannot answer, the question that is put. Some can be very 
  embarrassing. The one cited in the last paragraph </p>
  
  <p><strong>[1.]</strong>  [(for instance, in a 
  criminal trial, 'has the defendant done this before?')]  [<a href="https://law.stackexchange.com/q/9230/89">herefrom</a>]</p>
  
  <p><strong>[2.]</strong> would probably 
  lead to the discharge of the jury if the defendant did have any 
  previous convictions<br>
  <strong>[3.]</strong> since by refusing to answer the question the 
  jury would be bound to infer that he had, thus taking from the 
  defendant his right to anonymity of character. </p>
</blockquote>

<ol start="4">
<li><p>To me, 3 appears to be the Logical Fallacy of Appealing to Ignorance. So how would 3 imply 2? A refusal to answer the question does not logically imply a negative answer, though I understand why one may infer so.</p></li>
<li><p>What if it is the Judge who stops and prevents the witness from answering 1? Then the jury cannot infer anything about the witness. </p></li>
</ol>

<p>An appeal to ignorance asserts that a proposition is true because it has not yet been proven false. That is not in any way the situation here. The defendant knows if he/she has or has not so the only available answers under oath are "yes" or "no" - the jury knows this too so any other answer will be seen as disingenuous. However, this information (affirmative or negative) is off limits to the jury as it could prejudice their decision, hence the mistrial.</p>

<p>A quick judge could instruct the defendant not to answer and instruct the jury to disregard the question <strong>but</strong> if a conviction results the defence team could use the fact that it was asked as grounds for appeal. A judge must decide if the interests of justice are better served by a retrial or a tainted conviction.</p>

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