Interactionism operates on the assumption that objective, structural aspects of society do not accurately explain or predict societal behaviors. Instead, interactionism says that subjective elements of social interaction shape society. Basically, interactionist theorists maintain that humans are always adjusting their behaviors based on their interactions with other human beings, and not based on prescribed norms put forth by macrolevel social institutions such as governments or religious establishments.
Interactionists assert that people are actors--not passive observers--in their relationship to society. Interactionists believe that people are constantly reevaluating and adjusting the way they do life as a result of their daily interactions with other people.
A handful of people can react in dramatically different ways to the exact same person or idea. In addition, each individual reaction will likely change over time. Interactionism explains this via the basic assumption that people react to people and ideas based on the individual meanings they have assigned to them. These meanings are continually evolving based on daily interactions with other people.
Human beings use language as the primary means of interacting with one another. Therefore, interactionists believe that language is essential to the constant negotiation of individual meanings, thoughts and behaviors that shape society. Language need not be verbal. Symbols, body language and the written word are all included under the umbrella of language-based interactions.
According to the interactionist perspective, individuals adopt and perform various roles during any given interaction with other human beings. These roles are assumed based on social expectations that are generally determined by social position or status. For instance, women typically act out the socially prescribed role of "mother" by adopting caregiving behaviors toward their children.