There is sufficient evidence to show that a mitigating factor against mood disorder during the late LIA, has been the city walk. Quite apart from its therapeutic effect, in the case of both René Descartes and Immanuel Kant, the walking experience through seventeenth and eighteenth centuries' European streetscapes had thrust Descartes into his discovery of coordinate geometry, and Kant into his discernment of synthetic – a-priori concepts. In the nineteenth century the subjective experience of urban space has been also at the founding of European Existentialism. To Descartes orthogonally planned streets were the epitome of clear and distinct ideas as well as embryonic reference to axes x and y in a coordinate system. To Kant, according to some interpreters, direction in space was not absolute, but was the product of the body's encounter with space, leading him – through walking – to consider geometry not as a mere neutral a-priori standard of spatiality, but one into which synthetic subjectivity is injected.