“机械降神”这一说法来自希腊古典戏剧，指意料外的、突然的、牵强的解围角色、手段或事件，在虚构作品内，突然引入来为紧张情节或场面解围。在古希腊戏剧，当剧情陷入胶着，困境难以解决时，突然出现拥有强大力量的神将难题解决，令故事得以收拾。利用起重机或起升机的机关，将扮演神的下等演员载送至舞台上。这种表演手法是人为的，制造出意料之外的剧情大逆转。

拉丁语词组Deus ex machina（英译：God from the machine）翻译自希腊语ἀπό μηχανῆς θεός（apò mēkhanḗs theós），意思是机关跑出的神，中文一般翻译为舞台机关送神、机械降神、机器神、解围之神等。

这种手法通常被评论家认为是不高明的说书技巧，因为它破坏了故事的内在逻辑，纵使有时候会为了这个理由而故意采用。继亚里士多德之后，文艺复兴时期评论家将其视为一种迂拙的情节计策，虽然其仍然受用于文艺复兴时期的剧作家；莎士比亚将此计策用在《皆大欢喜》、《泰尔亲王佩力克尔斯》和《冬天的故事》。19世纪末，尼采批评欧里庇得斯透过这种计策将悲剧因素制造成乐观的类型，并促使他高度怀疑戏剧《blissful delight in life》是“希腊快乐”（Greek cheerfulness）。

尼采认为deus ex machina对苏格拉底文化恰好对症下药，重视文化知识过于酒神节的音乐并最终导致死亡的悲剧：

But the new non-Dionysiac spirit is most clearly apparent in the endings of the new dramas. At the end of the old tragedies there was a sense of metaphysical conciliation without which it is impossible to imagine our taking delight in tragedy; perhaps the conciliatory tones from another world echo most purely in Oedipus at Colonus. Now, once tragedy had lost the genius of music, tragedy in the strictest sense was dead: for where was that metaphysical consolation now to be found? Hence an earthly resolution for tragic dissonance was sought; the hero, having been adequately tormented by fate, won his well-earned reward in a stately marriage and tokens of divine honour. The hero had become a gladiator, granted freedom once he had been satisfactorily flayed and scarred. Metaphysical consolation had been ousted by the deus ex machina.

尼采认为，deus ex machina制造出虚假的慰藉感觉，这是不应该寻求的现象，这种情节计策的诋毁普遍出现在评论意见中。一些20世纪的修正主义者的评论，建议deus ex machina不能在简化的用语中被查看，并主张此种计策是凡人“刺探”与神的关系。拉什瑞姆（Rush Rehm）特别引用希腊悲剧的例子，其中deus ex machina提供复杂化角色的生活和态度，当面临神的同时为观众带来戏剧的尾声。