16.

To my mind, the clarification afforded by that ruling of the Court of First Instance makes a clear, useful contribution to the approach to the issue of reference to national law as it arises in this case. The criterion set out by the Court of First Instance is straightforward: the application of Community law may involve reference to national law, even where no express reference is provided for, where there is no possibility of defining the content and scope of the rule to be applied on the basis of Community law and its general principles. Let us consider the case before us. For my part, I am of the opinion that the question of interpreting the provision of Article 4(4) of the Regulation — as regards, of course, only its effects of relevance in this case — by taking account of the interpretative criteria which may be derived from the system, or the general principles of, Community law does not even arise. The reference to national law in the provision laying down the rule in question is not express but is certainly inherent in the ratio legis: it is a reference which may therefore be considered to be required, rather than permitted, by the aims pursued by the Community legislator itself. We are not in fact confronted with a provision designed to harmonize the rules laid down in this field at national level and to eliminate or reduce the differences between the various sets of legislation in force. Neither was Article 4(4) intended to be addressed to the Member States with a view to their making their treatment of the individuals concerned conform with any criterion to be found in the Community legal order. In contrast, what is involved is a rule specially laid down for Community staff who have left the services of the Communities which takes as the basis for its application the provisions, whatever they may be, laid down by the legislation which is relevant in each particular case in order to determine the income and social security contributions arising out of the newduties or employment of former members of Community staff. When it laid down that provision, the Community legislator was, moreover, aware that it was referring to legislative criteria which are likely to vary from one legal system to another and differ according to the legislative policy choices underlying in each system the determination of income and of the social security contributions which are to be deducted from income. Accordingly, the Regulation in question was adopted on the clear assumption that it was not appropriate to interfere with legislative assessments left to the national legislator and hence with the assessment of the solutions laid down by the national legal systems to which reference is made. The form of the reference is as we have seen: the intention was, in the final analysis, to recognize, or presuppose, that it is for each national legal system to establish a fair and reasonable proportion between income and social security contributions. The difference which may result from that solution as regards the treatment of former staff at Community level depending on the place at which they perform their new duties is therefore attributable to the provisions of national law, with which the Community rules do not seek to interfere.