A hypothesis is a flight design model, cobbled together with whatever struts and strings are available, and rolled out as a plausible proposition. It is a proposed reality model. It is a set of one or more assertive statements about existential structure or causal relationships, for which it is supposed that evidence might possibly be obtained. A hypothesis makes a claim in the here and now for its flight characteristics and stability prospects. It progressively acquires probability truth value only as evidence accumulates. Whilst it can exist for a while in the private domain of the hanger, eventually it must venture into the public arena, line up on the runway, and have it's credibility put to the test. A respectable hypothesis must be publicly testable.

Get the string and struts and fabric and glue to hang together, and fly in all weather, and there just might be an authority somewhere prepared to issue a certificate of factworthiness. Firstly a test program must be designed so as to progressively explore the flight envelope and operational characteristics. Next, a test-pilot must be chosen... one with extensive experience in the flying of kites, the floating of proposals and the stage-managing of official launches. Having faith in the hypothesis proposed would also be an advantage. Initial taxi-tests are then conducted and any parts which vibrate loose are retrieved under the cover of darkness and reattached out of sight of the press and any nosey stakeholders. Then, after the pre-flight checks have been completed...fuel, engine and controls... full power is applied and the prototype hypothesis is guided down the runway. The principal objective is to get above the tall grass at the end. As test-flight evidence accumulates and no unpleasant or fatal behaviour is encountered, a sympathetic certification authority just might be found to confirm the judgements and evaluations of the testpilot.

The set of statements of a hypothesis often suggest certain performance predictions. Perhaps there is an expectation that it will only use up half of the runway on take-off. Perhaps there is a claim that it will be impossible to stall. Whatever the predictions, the slightest bias whereby contrary performance characteristics are ignored or devalued is indicitive of the drift of the hypothesis towards a belief status. When this happens, any testing takes place more and more in the fantasy world of simulation and less and less in the demanding environment of turbulence and atmospheric extremes. With ever increasing computing power, hypotheses are now generally flown entirely in virtual reality. This technique ensures that numerous facts about the universe can be verified without the universe needing to know about it.