有关共同海损的定义,英国1906年《海上保险法》(MIA 1906)第66(2)条规定:There is a general average act where any extraordinary sacrifice or expenditure is voluntarily and reasonably made or incurred in time of peril for the purpose of preserving the property imperiled in the common adventure.与此规定相类似,规范共同海损理算和分摊的国际公约《约克-安特卫普规则》(York-Antwerp Rules)规则A规定:There is a general average when, and only when, any extraordinary sacrifice or expenditure is intentionally and reasonably made or incurred for the common safety for the purpose of preserving from peril the property involved in a common maritime adventure.据此,共同海损应当被定义为,在同一海上航程中,当船舶、货物和其他财产遭遇共同危险时,为了共同安全,有意而合理地采取措施所直接造成的特殊的牺牲、支付的特殊费用,由各受益方按比例分摊的一种法律制度。其构成要件应当包括:(1)同一海上航程中的财产遭遇了共同危险;(2)采取的措施必须是有意而合理的;(3)作出的牺牲和支付的费用必须是特殊的;(4)采取的措施必须有效果。而倘若船东在向海盗支付了赎金之后宣布共同海损,即就其所支付的海盗赎金向货主主张索赔,那么根据《约克-安特卫普规则》规则E(1)的规定,船东负有证明其索赔的损失或费用应当作为共同海损的举证责任,即船东必须证明其所支付的海盗赎金符合共同海损的构成要件。对此,笔者试将海盗赎金(支付海盗赎金的行为)与共同海损的构成要件比较分析如下: