英：chance;法：chance
弗洛伊德常常因其粗陋的决定论而遭人指责，因为他认为无论在表面上多么无关紧要的口误或过失，都总是不能归因于偶然。实际上，弗洛伊德曾经写道：“我相信外部（现实性）的偶然，那是千真万确的，而不相信内部（精神性）的意外事件。”(rcud, 1901:257)
拉康以他自己的措辞表达了同样的信念：在纯粹偶然性 (contingency)的意义上，偶然只存在于实在界。在象征秩序中，则根本没有纯粹偶然这样的事情。
在1964年的研讨班上，拉康借用亚里士多德在两种偶然之间的区分来阐明实在界与象征界之间的这一区分。在对因果性概念 (见：原因[CAUSE])进行讨论的《物理学》第二卷中，亚里士多德探究了偶然与命运在因果性中的角色。他区分了两种类型的偶然：“自发”(automaton)与“机遇”(yche), 前者指的是世界上一般而言的那些偶然事件，后者则指的是会影响有道德行为能力的施动者的那种偶然
他把“自发”重新界定为“能指网络”(the network ofsignifiers), 从而将其定位于象征秩序。这一术语因而便开始指代那些看似偶然的现象，但它们其实是能指在决定主体方面的坚持。“自发”并没有真正的任意性：唯有实在界才具有真正的任意性，因为“实在界是超越自发的”(S11,59).
实在界是与“机遇”排成一线的，拉康将其重新界定为“遭遇实在”(the encounter with the real)。“机遇”因而指的是实在界在象征秩序中的侵入：“自发”是决定着主体的象征秩序的结构，与此不同，“机遇”则是纯粹的任意性，超出象征秩序的决定。它是打断梦境的敲门声，而它在某种更加令人痛苦的水平上就是创伤trauma)。创伤性事件便是与实在界的相遇，是外在于意指的。
(chance) Freud has often been accused of a crude determinism, since no slip or blunder, no matter how apparently insignificant, is ever ascribed to chance. Indeed, Freud wrote,'I believe in extemal (real) chance, it is true, but not in internal (psychical) accidentalevents' (Freud, 1901:257).
Lacan expresses the same belief in his own terms: chance, in the sense of purecontingency, only exists in the real. In the symbolic order, there is no such thing as purechance.
In the seminar of 1964, Lacan uses Aristotle's distinction between two kinds of chanceto illustrate this distinction between the real and the symbolic. In the second book of the Physics, where the concept of causality (see CAUSE) is discussed, Aristotle explores therole of chance and fortune in causality. He distinguishes between two types of chance: automaton, which refers to chance events in the world at large, and tyche, whichdesignates chance insofar as it affects agents who are capable of moral action.
Lacan redefines automaton as 'the network of signifiers', thus locating it in thesymbolic order. The tem thus comes to designate those phenomena which seem to bechance but which are in truth the insistence of the signifier in determining the subject. Automaton is not truly arbitrary: only the real is truly arbitrary, since the real is beyondthe automaton' (S11,59).
The real is aligned with tyche, which Lacan redefines as 'the encounter with the real'. Tyche thus refers to the incursion of the real into the symbolic order: unlike theautomaton, which is the structure of the symbolic order which determines the subject, tyche is purely arbitrary, beyond the determinations of the symbolic order. It is a knockon the door that interrupts a dream, and on a more painful level it is trauma. Thetraumatic event is the encounter with the real, extrinsic to signification.