Summary The Open Science Proposal is that it would be useful for the scientific community to have a widely recognised Protocol of Openness, applying to individual scientific projects. Only a small fraction of all scientific projects would be done according to the required standard of radical openness, but those projects could claim a 'gold standard' of openness. Such projects would permit detailed scrutiny and criticism, and so furnish an efficient route to socially established reliable knowledge. Not all science is open, or even nearly open, nor is there any prospect of this. Four levels of openness are identified. If these four levels were borne in mind, controversial truth claims in science could be debated with more light and less heat.