Jacques Lacan posits a distinction between humans and other animals, that is, between 'human society' and 'animal society'.
The basis of this distinction is language; humans have language, whereas animals merely have codes.
As a result, animal psychology is entirely dominated by the imaginary, whereas human psychology is complicated by the additional dimension of the symbolic.
Lacan adopts the traditional anthropological opposition between nature and culture (culture being, in Lacanian terms, the symbolic order).
Like Claude Levi-Strauss and other anthropologists, Lacan points to the prohibition of incest as the kernel of the legal structure] which differentiates culture from nature.
"The primordial Law is therefore that which in regulating marriage superimposes the kingdom of culture on that of a nature abandoned to the law of mating."
The regulation of kinship by the incest taboo points to the fact that the paternal function is at the heart of the rift between humans and animals.
By inscribing a line of descent from male to male and thus ordering a series of generations, the father marks the difference between the symbolic and the imaginary.
In other words, what is unique about human beings is not that they lack the imaginary dimension of animal psychology, but that in human beings this imaginary order is distorted by the added dimension of the symbolic.
The imaginary is what aniamls and human beings have in common, except that in human beings it is no longer a natural imaginary.
Hence Lacan repudiates "the doctrine of a discontinuity between animal psychology and human psychology which is far away from our thoughts."
On the other hand, Lacan also uses the term 'nature' to denote the idea that there is a 'natural order' in human existence.
This great fantasy of nature underlies modern psychology, which attempts to explain human behavior by reference to ethological categories such as instinct and adaptation.
Lacan is highly critical of all such attempts to explain the phenomena in terms of nature.
He argues that they are based on a failure to recognize the importance of the symbolic order, which radically alienates human beings from natural givens.
In the human world, even "those significations that are closest to need, significations that are relative to the most purely biological insertion into a nutrittive and captivating environment, primordial significations, are, in theri sequence and in their very foundation, subject to the laws of the signifier.
Lacan thus argues that "the Freudian discovery teaches us that all natural harmony in man is profoundly disconcerted."
There is not even a pure natural state at the beginning in which the human subject might exist before being caught up in the symbolic order.
Need is never present in a pure pre-linguistic state in the human being: such a 'mythical' pre-linguistic need can only be hypothesized after it has been articulated in demand.
The absence of a natural order in human existence can be seen most clearly in human sexuality.
Freud and Lacan both argue that even sexuality, which might seem to be the signification closest to nature in the human being, is completely caught up in the cultural order; there is no such thing, for the human being, as a natural sexual relationship.
One consequence of this is that perversion cannot be defined by reference to a supposed natural or biological norm governing sexuality.
Whereas animal instincts are relatively invariable, human sexuality is governed by drives which are extremely variable and do not aim at a biological function.