同质说（Consubstantiation），亦称为合质说或圣体共在论，[1]是基督教神学中有关圣体实在的理论之一。与圣餐变体论（Transubstantiation）相反，它相信圣餐礼中基督的肉与血是和面包与酒同在的，而不是通过弥撒转换而成的。此学说是罗拉德派的核心思想之一，天主教视其为异端。一些信义宗信徒与牛津运动者认同这种观点，但教会、认信文和护教学家都不赞成[2][3][4]；信义宗将其圣餐观称作“真实临在”说，差异为前者可能包含“基督的血与葡萄酒物质上混合在一起”的教导，而后者认为“主基督真正的身体和血，在饼和酒之中，亦在饼和酒之下”，不与物质实体相混但又真实临在[5]。
在早期教会中也存在类似观点。150年左右游斯丁就曾说过：“这些被神祝福过的、滋养我们的血与肉的食物（面包和葡萄酒）也是肉身化的耶稣的血与肉”。[6]
《宗教改革对礼仪的
影响与反思》，天国事齐探讨：宗教改革五百年，页14
Formula of Concord, Epitome, VII.42 and Solid Declaration VII.127 in F. Bente, Triglot Concordia, (St Louis: CPH, 1921), 817, 1015.
Real Presence Communion – Consubstantiation?. WELS Topical Q&A. Wisconsin Evangelical Lutheran Synod. [26 Jan 2015]. （原始内容存档于2008-01-02）. Although some Lutherans have used the term 'consbstantiation' [sic] and it might possibly be understood correctly (e.g., the bread & wine, body & blood coexist with each other in the Lord's Supper), most Lutherans reject the term because of the false connotation it contains...either that the body and blood, bread and wine come together to form one substance in the Lord’s Supper or that the body and blood are present in a natural manner like the bread and the wine. Lutherans believe that the bread and the wine are present in a natural manner in the Lord’s Supper and Christ’s true body and blood are present in an illocal, supernatural manner.
Lectures on the Augsburg Confession. Theological Seminary of the United Lutheran Church in America (Lutheran Publication Society). 1888: 350 [13 June 2014]. （原始内容存档于2021-03-11）. But in neither sense can that monstrous doctrine of Consubstantiation be attributed to our church, since Lutherans do not believe either in that local conjunction of two bodies, nor in any commingling of bread and of Christ's body, of wine and of his blood.
