1. A decision by a court must be reasonably explained:
(i). Section 174 of the Criminal Justice Act 2003 states:
"any court passing sentence on an offender—
(a) must state in open court, in ordinary language and in general terms, its reasons for deciding on the sentence passed"

(a). While this mentions sentencing, the same principle is understood and accepted also to apply to any other decision by a court.
(ii). Section 10 of the Tribunals and Inquiries Act 1992 states:
"...it shall be the duty of the tribunal or Minister to furnish a statement, either written or oral, of the reasons for the decision if requested, on or before the giving or notification of the decision, to state the reasons."
2. This means, and this is a fact not disputed by the courts and Parliament, a decision by a court is not lawful if:
(i). It is not explained at all or
(ii). if the explanation provided is unreasonable or untrue.
3. The Court of Appeal, in Flannery v Halifax Estate Agencies Ltd [2000], established that the duty to give reasons "is a function of due process, and therefore of justice": it ensures parties understand why they won or lost, and it concentrates the judge's mind to produce sound decisions.
3. Article 6 of the European Convention on Human Rights is often cited as requiring courts to provide clear and rational decisions, and the European Court of Human Rights has interpreted it that way - for example: Ruiz Torija v. Spain (1994).
(i). I have been unable to discern any traces of such a requirement in that Article of law.
(ii). While such a fancy might be comforting for some, I have to admit such an interpretation is more likely the product of desperate wishing married with careless reading of the law: if you would find that requirement in that Article, you might just as easily find all other kinds of stipulation in that and other articles of law, for which you might care a lot less.
(ii). The Court at Strasbourg having decided this is a legal requirement, however, and caselaw being what it is, it still means a petition before that Court, which cites the principle previously expressed by that Court and not subsequently repudiated by the same court, or which particularises a judgement by that court, demanding such an explanation, must be answered either with such an explanation or with a reason why an unexplained judgement would be handed down.
3. I hope I have established the legitimacy of this Principle - that decisions by courts be explained rationally - and its vital importance for justice: what happens when courts make decisions for unknown and or unknowable reasons, when unreasonable decisions by the courts are deemed legitimate, when the courts may justify their decisions with lies?