Communication (from Latin commūnicāre, meaning "to share") is the act of conveying intended meanings from one entity or group to another through the use of mutually understood signs and semiotic rules.
Marketing is the study and management of exchange relationships. Marketing is used to create, keep and satisfy the customer. With the customer as the focus of its activities, it can be concluded that Marketing is one of the premier components of Business Management - the other being innovation.
Psychology is the science of behavior and mind, including conscious and unconscious phenomena, as well as feeling and thought. It is an academic discipline of immense scope and diverse interests that, when taken together, seek an understanding of the emergent properties of brains, and all the variety of epiphenomena they manifest. As a social science it aims to understand individuals and groups by establishing general principles and researching specific cases.
Give them quality. That's the best kind of advertising in the world.
Milton Hershey. Interview with Abe Heilman, 1953. Paul Wallace Research Collection, Accession 97004, Box 2, Folder 24; Hershey Community Archives, Hershey, PA, USA.