違法無效合同不當得利返還的比例分擔：以股權代持為中心

關於違法無效合同的不當得利返還，我國法並無明確規定。兩大法系大同小異的做法是「全有全無」，具體為不當得利的違法性抗辯及例外規則體系。我國《民法典》在編纂過程中雖然刪除了不法原因給付規則，但仍可通過對第985條的擴張解釋，將「全有全無」設定為違法無效合同不當得利返還的一般規則。我國司法實踐則沿襲了最高人民法院在股權代持糾紛中所持的裁判立場，基於對原《合同法》第58條的擴張解釋，在投資已有增值且國家不予收繳的前提下，採取了在受損人與得利人之間進行「比例分擔」的返還方案。英國法從形式主義轉向結果主義的最新發展、量化修正的比例原則、股權代持中當事人經營行為的存在，三者共同證立了違法無效股權代持適用「比例分擔」特殊規則的正當性;但這項特殊規則不應替代「全有全無」，上升為普適於各類違法無效合同不當得利返還的一般規則。無論是「全有全無」還是「比例分擔」，不當得利返還對象原則上不應包括金錢的使用價值。

"Chinese law currently has no clear answer to the question of restitution for unjust enrichment involving illegal and void contracts. The prevailing position in both common law and civilian jurisdictions, despite minor discrepancies, is the ''all or nothing'' approach, represented by the system of illegality defence to unjust enrichment. Although the draft provision specifically on the illegality defence has been deleted in the final version of the Chinese Civil Code, the ''all or nothing'' approach nevertheless re-mains to be the general rule for illegal and void contracts in Chinese law by an extensive interpretation of Article 985. By contrast: in the context of shareholding entrustment, the position in Chinese commercial law is ''apportionment'' of restitution between the enrichee and the aggrieved party, which derives from the Supreme People's Court's position in handling issues of illegal and void shareholding entrustment. This position is based on an extensive interpretation of Article 58 of the Contract Law, and is qualified by the existence of investment appreciation, and by the non-application of forfeiture. The application of the special rule of ''apportionment'' in the context of illegal and void shareholding entrustment can be justified by a range of factors, namely, the very recent development in English law regarding its shift from formalism to consequentialism, the principle of proportionality modified by quantitative ideas, and the existence of the parties' management activities in shareholding entrustment. These factors also demonstrate why such special rule of ''apportionment'' should not be upgraded to replace the general ''all or nothing'' rule, therefore applies to all kinds of illegal and void contracts. Whether ''all or nothing'' or ''apportionment'' is applied, the scope of restitution for unjust enrichment shall not, in principle, cover the use value of money."