The dual relation is (French:relation duelle) a basic feature of the imaginary order.
The dual relation is the relation between the ego and the specular image which Lacan analyzes in his concept of the mirror stage.
The dual relation is always characterised by illusions of similarity, symmetry and reciprocity.
In contrast to the duality of the imaginary order, the symbolic order is characterised by triads.
In the symbolic order all relations involve not two but three terms; the third term is the big Other, which mediates all imaginary dual relations.
The illusion of reciprocity in the imaginary dual relationship contrasts with the symbolic, which is the realm of 'absolute non-reciprocity.'
The Oedipus complex is the paradigmatic triangular structure, since the father is introduced into the dual relation between mother and child as a third term.
The Oedipal passage from a dual relation to a triangular structure is none other than the passage from the imaginary to the symbolic order.
Indeed, the very concept of structure itself involves a minimum of three terms; "there are always three terms in the structure."
The opposition between imaginary dyads and symbolic triads is complicated by Lacan's discussion of the 'imaginary triad.' The imaginary triad is Lacan's attempt to theorise the preoedipal stage in terms other than those of a merely dual relationship, and refers to the moment preceding the Oedipus complex, when a third element (the imaginary phallus) circulates between the mother and infant. When the father intervenes in the Oedipus complex he can therefore be seen either as a third element (between mother and child) or as a fourth element (in addition to mother, child and phallus). It is for this reason that Lacan writes that in the Oedipus complex "it is not a question of a father-mother-child triangle, but of a triangle (father)-phallus-mother-child."
One of Lacan's most frequent criticisms of the psychoanalytic theory of his day is that it constantly fails to theorise the role of the symbolic, and thus reduces the psychoanalytic encounter to an imaginary dual relationship between analyst and analysand.
In particular, it reduces analytic treatment to an ego-to-ego encounter which, because of the aggressivity inherent in all imaginary dual relations, often degenerates into a 'fight to the death' between analyst and analysand, a power struggle in which they are 'at daggers drawn.'
Against such a misconception, Lacan insists on the function of the symbolic in the analytic process, which introduces the Other as the third term in the analytic encounter. "It is within a three- rather than two-term relation that we have to formulate the analytic experience." Rather than seeing the treatment as a power struggle in which the analyst must overcome the patient's resistance, which is not psychoanalysis but suggestion, the analyst must realise that both he and the patient are equally subjected to the power of a third term: language itself. Lacan's rejection of duality can also be seen in his rejection of all dualistic schemes of thought in favour of triadic schemes; "all two-sided relationships are always stamped with the style of the imaginary." For example instead of the traditional binary opposition between what is real and what is imaginary, Lacan proposes a tripartite model of real, imaginary and symbolic.
Other such triadic schemes are the three clinical structures of neurosis, psychosis and perversion; the three formations of the ego (ego-ideal, ideal ego and superego); the triad nature-culture-society; etc. However, as if to counteract this trend, Lacan also emphasised the importance of schemes involving four elements (see quaternary).