A great number of researchers contributed to the argument that what distinguishes human from beast. To save space on the screen, I will not even enumerate all the possible authors and their versions.

I was once interested in the idea of Boris Porshnev, described in his fundamental book "Paleopsihology." There, he convincingly argued that having a language, developed as a communicative tool, distinguishes humans from animals. However, current studies indicate that the presence of rudimentary languages have higher primates, and in cetaceans, and rats, so the distinction to draw here is more complicated.

Obviously, man has developed more abstract thinking than animals, but by repeating Porshnev's question - "What is the unambiguous distinction between human and animal?", It makes sense to us to investigate the processes of constructing a man of abstract images - signs.

Signs studying by semiotics, obviously, being a meta to linguistics, since the characters are reflected in language.

In semiotics taken (by Yuri Lotman) identified three major subsections: semantic, syntactic and pragmatic.

Semantics, study the process of constructing, abstractisation, mark its transition from the image of the object of the world in to abstract form, a sign. With well-known stretch of the imagination, one can say that animals can make abstractisation of their experience - for example, recognize the situation as "dangerous" and give this another sign of his brethren.

It also allows to speak about certain manifestations of pragmatics, in animal behavior - they recognize the signs of their kinsmen and react to them.

But syntactics studying the interaction between characters within the text ... Here it is interesting turns. Indeed, the construction of sign systems - from alphabets to cultures has only homo sapiens sapiens. And to  perceive, to process, to combine and to abstract the relationship between characters, can only make a human too. Building signs TEXTS  can also just humans.

So it is possible to conjecture that it is the ability to manage sign systems, the syntactic, is a real distinguishes human thought from the animals.