Why did Lord Reid write &quot;we should beware of looking at older authorities through modern spectacles&quot;?
<p>Appellate judges usually aren't stupid or short-sighted. They can foresee that their judgments will become "older authorities" and will be read through "modern spectacles". So what did Lord Reid mean exactly? </p>

<p><a href="https://www.amazon.co.uk/Public-Law-Text-Cases-Materials/dp/0198820283/ref=dp_ob_title_bk" rel="nofollow noreferrer"><em>Public Law: Text, Cases, and Materials</em> (2019 4 edn)</a>. p 317.</p>

<blockquote>
  <h2>The <em>Burmah Oil</em> case</h2>
  
  <p>In March 1942, the British army blew up the installations and oil stocks owned by the Burmah
  Oil Company at Rangoon in order to prevent them from falling into the hands of the advancing
  Japanese forces. The Burmah Oil Company later sought compensation from the Crown
  for its losses. In the House of Lords, it was accepted that the actions were done under the royal
  prerogative and the question was whether compensation had to be paid. The House held by a
  three- to- two majority that, in the circumstances, compensation was payable. Controversially,
  the effect of the decision was subsequently retrospectively reversed by the War Damages Act
  1965. For now, our interest focuses on Lord Reid’s judgment.</p>
  
  <h2><em>Burmah Oil Company v Lord Advocate</em></h2>
  
  <p>[1965] AC 75, 99–100</p>
  
  <blockquote>
    <h3>Lord Reid</h3>
    
    <p>It is not easy to discover and decide the law regarding the royal prerogative and the consequences
    of its exercise. Apart from <em>In re a Petition of Right</em> [[1915] 3 KB 649] and <em>Attorney-General v De Keyser’s Royal Hotel Ltd.</em> [[1920] AC 508] there have been no cases directly
    raising the matter for some centuries, and obiter dicta and the views of institutional writers
    and text writers are not always very helpful. The definition of Dicey [. . .] always quoted with
    approval [. . .] does not take us very far. It is extremely difficult to be precise because in former
    times there was seldom a clear- cut view of the constitutional position. <strong>I think we should beware
    of looking at older authorities through modern spectacles</strong>. We ought not to ignore the
    many changes in constitutional law and theory which culminated in the Revolution Settlement
    of 1688– 89, and there is practically no authority between that date and 1915. I am no historian
    but I would suppose that Maitland is as good a guide as any. In his Constitutional History
    he says: ‘I do not wish you to think that a definite theory to the effect that while legislative
    power resides in king and parliament, the so- called executive power is in the king alone, was
    a guiding theory of mediaeval politics. On the contrary, the line between what the king could
    do without a parliament, and what he could only do with the aid of parliament, was only drawn
    very gradually, and it fluctuated from time to time.’ (p. 196.) [. . .] So it appears to me that we
    must try to see what the position was after it had become clear that sovereignty resided in
    the King in Parliament. Any rights thereafter exercised by the King (or the executive) alone
    must be regarded as a part of sovereignty which Parliament chose to leave in his hands. There
    is no doubt that control of the armed forces has been left to the prerogative (see Chandler v
    Director of Public Prosecutions subject to the power of Parliament to withhold supply and to
    refuse to continue legislation essential for the maintenance of a standing army: and so also
    has the waging of war. But it may be interesting to note in passing the Scottish Act, 1703, c. 5,
    which provided that ‘no person being King or Queen of Scotland and England shall have the
    sole power of making war with any prince, potentate or state whatsoever without consent
    of Parliament [. . .]’</p>
  </blockquote>
</blockquote>

<p>p 318.</p>

<blockquote>
  <p>&nbsp; &nbsp; The reason for leaving the waging of war to the King (or now the executive) is obvious. [. . . although
  . . . t]here is difficulty in relating the prerogative to modern conditions. In fact no war which
  has put this country in real peril has been waged in modern times without statutory powers of
  an emergency character. [. . .]</p>
  
  <blockquote>
    <h3>QUESTIONS</h3>
    
    <ol>
    <li>Why does Lord Reid say that ‘we should beware of looking at older authorities through
    modern spectacles’?</li>
    </ol>
  </blockquote>
</blockquote>

<p>I would argue that he wrote it in keeping with the saying "say what you mean, and mean what you say."  This passage discusses the difficulty of inferring constitutional principles from old authorities that were written during a time when constitutional thinking had not yet arrived at the "modern" position.  In this case, he is considering the evolution in the constitution between the 17th and 20th centuries.</p>

<p>The opening paragraph of this question considers that someone <em>today</em> might have to apply the same caution when looking at Lord Reid's opinion, but that does not appear to be Lord Reid's concern.  He is more concerned with his own viewpoint as he considers authorities from several centuries ago than he is with the implications for future opinions that rely on his own.  After all, his main duty is to reach an opinion in the case at hand.</p>

<p>Still, one can imagine that Lord Reid would have recognized the possibility, or even the probability, that a 23rd-century judge would need to read 20th-century opinions with similar caution because of future constitutional change.</p>

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