Ratio Decidendi

Conversely "ratio decidendi" of a case consists of the material facts of such case and the decision made through the judge on the basis of those facts.  So hence material facts become the basis or "rationale" or like ratio upon that such the judge are to decide (decidendi) the case.  However they constitute, the way in ordinary parlance, the reason, or ground, of the judge's decision and to ensure that decision-making process is the rational one also.

Therefore ratio decidendi of a decided such case constitutes the legal rule, or the principle, just to the decision of future cases with similar material facts.  Thus in other words their decision is a precedent to be followed where deciding such cases.