Two key concepts in the scientific approach are theory and hypothesis.
Theories and Hypotheses
A theory is a well-developed set of ideas that propose an explanation for observed phenomena that can be used to make predictions about future observations. For example, the theory of evolution by natural selection in biology is a well-developed explanation for how genetic characteristics change through generations. In psychology, there are theories about child development, about how people act in social situations, about why we experience certain emotions, and more.
A hypothesis is a testable prediction that is arrived at logically from an observation. It is often inspired by a theory. The results that come from testing the hypothesis may lead to theories being adjusted or modified. A hypothesis is often worded as an if-then statement (e.g., if I study all night, I will get a passing grade on the test).


If you walked out of your home and discovered a very aggressive snake waiting on your doorstep, your heart would begin to race and your stomach churn.

According to the James-Lange theory, these physiological changes would result in your feeling of fear. A hypothesis derived from this theory might be that a person unaware of the physiological arousal that the sight of the snake elicits will not feel fear.
Some individuals who suffer significant injuries to their spinal columns are unable to feel the bodily changes that accompany emotional experiences. Therefore, we could test the hypothesis by determining how emotional experiences differ between people who have the ability to detect these changes in their body and those who do not. In fact, this research was conducted—it turns out that while the emotional experiences of people who are unaware of their physiological arousal may be less intense, they still experience emotion (Chwalisz, Diener, & Gallagher, 1988). This particular research study did not support the hypothesis—even without being physiologically aroused, people still experienced fear.