The rationale is set out in pragmatic terms in Ursula Becker v Finanzamt Münster - Innenstadt [1982] CJEU (Case 8/81) as follows: `... in cases in which the Community authorities have,
by means of a directive, placed Member States under a duty to adopt a
certain course of action, the effectiveness of such a measure would be
diminished if
persons were prevented from relying upon it in proceedings before a court....»