In psychological science, there are different approaches, or perspectives, different people bring to the field. As a science, psychology is descriptive. A true scientist doesn't actually 'prove' anything, they use methodological rigor to seek a consistent result under a particular set of circumstances.
Truth is consistency.
These results then serve as evidence to theories. These theories are what most people think of when describing findings. 'Study shows that sleep is important to memorization.' Well, yes and no. The study showed that people scored higher on a test if they slept beforehand. We extrapolate from that that sleep is important to memorization. (Alternative extrapolations could include: sleep reduces stress, sleep deprivation impairs general functioning, etc. These possibilities are narrowed down by repeating testing the same hypothesis with different methods that control for alternative explanations.)
But then comes the question of how. And in attempts to explain multiple findings and multiple theories, psychologists develop models. Although few scientists will disagree with the raw data of a well-designed study, they may disagree on which model best accounts for results in the larger scheme. Models are statistically tested for goodness of fit, which helps lend some objective credence to them, but ultimately they are based on incomplete information. Most of these models are focused on a concept, and highly abstracted, such as the various models of memory. They look kinda like this. Here's a more detailed explanation of one you may be familiar with.
