The basic assumption for science is the rule of logic when a phenomenon arise. The rules of logic depends on reasoning. This means researching any assumption or hypothesis to prove it or nolify it. This rule may be applied to any major, including psychology.
To give a simple example on psychology: two persons have promoted relations between them. One of the partners looks angry and tired. Assumptions to understand the situation, is to give certain possibilities for the mode of the partner. Usually some people think they know what makes the partner angry and tired, but may be remove the main cause. So judgmental opinion is not scientific or logical. The best way to ask the right question and get the right answer.
In any other major, the same rule or method is followed. Any scientific process follows these steps to be logical or reasonable or scientific:
1) ask the question
2) give assumptions or hypotheses for investigation
3) find the best research method to answer the question(s)
4) find a valid and suitable sample to distribute a questionnaire to collect data necessary to be tested
5) making measures to test the hypotheses
6) testing the correlation in a cause effect relations
7) finding the results of measurement, which hypothesis was rejected or accepted
8) reporting the finding includes the results of the scientific study and recommendations to deal with the problem we asked about in step 1.
9) explaining limitations or errors happened in the serach process to be more logical.
10) taking the true understanding of the phenomenon may be generalized to the population.
One note cane be made here to warrant scientific methodology, where any phenomenon in Humanities has to be connected to time and space, there fore, the study or any study is limited and controlled by the two factors. Because both time and space are continually changing . Therefore, the scientific method is limited to time and space where the study takes place.
Thank You for the good question you ask, Stephanie.
Hasan Yahya, Ph.Ds