Usually a hypothesis passes four stages:
the first stage can be called speculation; the second is the empirically tested hypothesis,
which is only valid for the explanation of a single phenomenon; at the third stage
hypotheses are grounded on a connection to existing knowledge that has not yet been
tested. Hypotheses at the fourth stage are called reliable. They have proven to be
worthwhile in multiple empirical tests. A reliable hypothesis that has a general scope
as well is called a law or a statement of invariance .105