Perspectives are deeply personal and vary from person to person, whereas theories are shared paradigms. Theories are collective, academic models shared by individuals within and across academic disciplines. Feminist theory, for example, emphasizes the role of socially constructed gender expectations in everything from literature to world history. Postmodernist theory examines sociological and anthropological questions by asking how communities socially construct notions of truth. Theory develops over time through academic discourse. Perspectives develop through individual experience.
A person's perspective can change instantly, based on one profound experience. The atheist who has a vision of seeing the divine can change quickly into a devout mystic. A child who observes his parent inflicting violence upon another parent will have an immediately different perspective on the abuser's character. An individual cannot change or create a theory. Academics engage in several years of discussion via conferences, journals and academic papers before accepting a new theory as a legitimate mode of academic inquiry.
In professional and intellectual life, most people use a combination of theory and perspective to make choices about which questions to pursue and which actions to take. A clinical psychologist, for example, will be influenced by certain dominant psychological theories concerning behavior modification, personality development and mental health. Yet she will also lean upon her personal perspective, informed by experiences with similar clients and her values and assumptions.
Certain theories have become so pervasive that it's hard to keep in mind that people didn't always consider them respectable. Scientific theories once held in disrepute have grounded the work of scientists for centuries. For example, Albert Einstein's theories of special relativity and general relativity have risen from social obscurity to become cornerstones of modern science. Similarly, individual perspectives have changed drastically in a mere lifetime. During the civil rights era of the 1950s and 1960s, nonviolent civil disobedience influenced many racially prejudiced individuals to alter their perceptions concerning questions of racial equality.