1607 BC: The composer Monteverdi composed the musical work called Orpheus. This marks a moment when the symbolic models supported image models in music. In the same period, the "recipe" to compose a fugue was also established. Europeans invented the polyphonic music. 1614 BC: the logarithms are introduced in mathematics. 1640 BC: Rene Descartes, scientist He considers that the world can be understood based on mathematics. This is a higher level in the developing of the symbolic models. Mathematics is based on symbolic models only. In fact, any specific field of mathematics is a symbolic model. But, a symbolic model from mathematics cannot be used in a direct way to understand the external reality. Newton's mechanics appeared at first as a logical model, and then it was translated to a mathematical form. Mathematics generates only numbers. They have no meaning without the calibration of the model. To calibrate a model means to interact with external reality and so, to go beyond the limits of mathematics. The normal interaction with external reality of a symbolic model from mathematics is: prediction > comparison with external reality > change of the model > a new prediction. This loop has to continue as many times as needed, so that the difference between the prediction and the external reality becomes acceptably low. It seems that Descartes did not understand this. This problem seems to be difficult to be understood even in our days, taking into account that the mathematician Godel "proved" the existence of God, without any interaction with external reality. 1642 BC: Rembrandt van Rijn, the painter Rembrandt marks a moment when the human brain reaches a peak in building and operating image models. 1687 BC: Newton's Mechanics After Euclid's Geometry (about 2000 years ago) this is the second fundamental symbolic model created by the human mind. It is a big step in the evolution of the brain. Starting with Newton, the development of the capacity to build and operate symbolic models accelerates, and this process continues today. Newton is not well understood even in our days. Some dictionaries say that Newton discovered the law of gravity. This law was introduced by Newton to save his theory. The inertia principle states that any material body, which is left free, is moving in a straight line, with constant velocity to infinity. But in the external reality such a phenomenon is not met. The planets are moving on closed trajectories in space. The only solution to save the theory was to invent a new force, which was called "gravity". Einstein, for instance, says that gravity does not exist. The apparent attraction between the material bodies is generated by the change of the shape of the space. He is able to explain some phenomena which cannot be understood based on the Newton's gravity (the precession of the planet Mercury, e.g.).