The intelligence of animals is marvellous; their communication by signs is extremely refined, nobody can deny it. How can one defend the opinion that animals cannot think? My thesis: The mental activities of animals can be explained as psychological processes, they cannot be subsumed under the norms of logics, they are not true or false, they don't contradict each other, they are not necessarily affirmative or negative. By this, thinking activities of men are different from the intelligence of animals
.