Cognition: a tool for reinforcing security in software defined networks. Security is one of the most important requirements for networks and serious concerns for network providers and users. Software Defined Networking offers to network managers new opportunities for deploying efficient security mechanisms. By means of applications and controller functionalities, SDN is able to provide a highly reactive network security monitoring, to perform comprehensive traffic analysis, and to enforce fine-grained dynamic access policies. In the present work, we show how such security mechanisms can be further enforced by applying cognitive functions at the SDN application plane. The proposed approach that finds its foundation into the control loops applied in Autonomic Managers Networks (AMNs), can efficiently enable secure and safe SDN scenarios.