Yes, you must! That is not to say you can just state a hypothesis and posit it with no argument at all. For each hypothesis, develop an argument about the sign of the relationship. Start with the argument, and end your paragraph with the literal statement of the hypothesis, as a conclusion.

The argument is more than a phrase like ‘Previous research has shown that X is positively related to Y’. Obviously the results of previous research include important information, but they are not an argument for a hypothesis; they may support a specific argument about why X influences Y.

Also the basis for a hypothesis is more than the statement that you expect it to be true ‘because it is logical’ or that it is ‘common sense’. Neither is it enough to summarize previous research supporting the hypothesis. A hypothesis may not have been tested at all in previous research. It is not necessary for a hypothesis to be supported by previous research. What matters is whether the argument is sound, and preferably based on a theory.

A proper argument takes the form of a syllogism. The syllogism is a logical form consisting of a General Law, an assertion about specific Conditions, and a Hypothesis. The Hypothesis is the conclusion drawn from the combination of the General Law and the assertion about specific Conditions.

An example of a general law is: the stronger a person is attached to a group, the more likely that this person follows the norms in this group. An example of a condition is: church attendance indicates attachment to a religious group. The resulting hypothesis is: the higher the frequency of church attendance of a person, the higher the likelihood that this person follows the norms within the church. You can test this hypothesis for different forms of behavior that religious groups have norms about, such as monetary contributions to the group, or voting behavior. Additional conditions specify these norms: religious groups proscribe that their members should contribute time and money to the benefit of the group.

Sometimes there are valid arguments for a positive as well as a negative relationship between two variables. In that case try to reason which direction is the strongest. The empirical test will tell you which effect dominates. If there is no way to tell which one is strongest, consider phrasing two alternative hypotheses.

“Can I posit a hypothesis when there is no previous research on it?”

Most certainly, yes. A hypothesis follows from a theory. It may have received support in previous research, but is also possible that no one has tested it before. It is also possible that you’ve been searching for previous research using the wrong keywords, that is: using lay terms that are not used in academic research. If you’re sure that no one has tested your hypothesis before, you have an argument in favor of the scientific relevance of your study.