The author has tried to prove the relevance of the time and space factor in the positions of subjects and predicates in premises for drawing correct conclusions in deductive reasoning. He used three types of inferences: A. Inferences from premises containing concrete concepts. B. Inferences from premises using graphic concepts (capital letters). C. Inferences from premises with Christian names. Each of these types was further subdivided into two different types: a) The subjects and predicates in the premises «were, for the purpose of inference, more distant in time and space (example: The wardrobe is to the right of the door. The stove is to the right of the wardrobe. What is on the left, in the middle, on the right?), b) The subjects and predicates were not very distant in time and space for the inference (example: The chair is to the right of the table. The window is to the left of the table. What is on the left, in the middle, on the right?). The third type C corresponded to the classical inferences of Burt’s: The colour of Olga’s hair is lighter than that of Mary’s. The colour of Olga’s hair is darker than that of Vera’s. Which of the three girls has the darkest hair? This type also included types a) and b) (see above). Irrespective of the children’s age the “a )” type was more difficult than type “b)” , on the level of 5 per cent according to the t-test, which was statistically significant. The form of subjects and predicates in the premises proved to be unimportant because the differences between types A, B and C were statistically insignificant, but what proved to be important was the time and space factor in the positions of subjects and predicates in premises for inference. The curves of development showed two peaks on the way up, one around the age of ten, the other at about thirteen years of age, which means that the development of both forms of inference is going on in leaps. At the age of eight the children already gave 45.7 per cent of correct answers, the twelve-year-olds gave 74.4 per cent and the fifteen-year-olds 86.3 per cent correct answers. Children are capable of reasoning in this form even before the age of twelve.