George Herbert Mead, a professor at the University of Chicago who never published his theory while alive. Blumer is one of his students who believed in his work and compiled it, added to it, and published it after Mead's death.
The theory of symbolic interactionism is an
interpersonal theory, based on three core principles: meaning, language and thought.
Meaning is the construction of social reality. We act differently to people and things based on the meanings that we assign to them. Once people define a situation as real, the consequences are real as well.
Language is the source of meaning. Meaning is negotiated through interactions which require language. People have the power to name things, but names and symbols are just signs with no inherent relation to what they point to. For instance, the letters dog, and the sound of the word dog has nothing to do with the actual creature. There is no link except for the language that we created. By communicating with other people and creating words for objects we create a universe of discourse.
Thought is when we take the role of the other. This process is called minding and is an inner conversation, where we sort things out in our head and give things meaning. Unlike other animals, humans have the ability to take the role of the other and predict the outcome of what they say and do.
Another related principle is the self. We can only find ourselves by taking the role of the other, by imagining what we look like in someone else's perspective. This is called looking-glass self. The self is always changing and before a person can conscious of the self, they need to belong to a community. The self is a combination of unorganized and unpredictable aspects of life (the "I") and the image of yourself seen through the looking-glass self and people reactions to your behavior and speech (the "me").