The case for a posteriori hypotheses to fuel scientific progress.

A priori hypotheses are considered a cornerstone of the scientific method. A posteriori hypotheses, on the contrary, are judged by many as inappropriate and are hardly ever acknowledged as such. Such practice is inadequate. This paper advocates the value of clearly stating a posteriori hypotheses as the result of advanced thinking in the course of a scientific study. In few cases, modified explanations of observed phenomena may be tested within the same study from which they originate. In most cases, a posteriori hypotheses as a result of abandoning part of a priori thinking in the light of new observations will have to be tested in future studies. And yet, their unambiguous formulation in the study publication can enable others to follow up on the findings and the modified conjectures fast and thus facilitate scientific progress. In this vein, a posteriori hypotheses should be encouraged as a thinker's prime tool rather than be discouraged. Indeed, it is suggested, that information on a posteriori hypotheses should be formally required when research is published.