The origins of projectivism lie with David Hume, who describes the view in Treatise on Human Nature: "Tis a common observation, that the mind has a great propensity to spread itself on external objects, and to conjoin with them any internal impressions, which they occasion, and which always make their appearance at the same time that these objects discover themselves to the senses.
Because one observes events of this type, one is led by induction to suppose that like causes will result in like effects, and from this one infers the notion of causation.
Non-cognitivists, on the other hand, believe that moral claims are not truth-apt—not capable of being true or false.
[4][5][page needed] As a non-cognitivist, the projectivist holds that ethical judgments are the product of conative, rather than cognitive psychological processes.
Blackburn's projectivism, which he calls quasi-realism, is based on the significance of the conative stances that are held.
His idea is that these conative stances are the starting point for what the meta-ethical realist labels beliefs or even facts, like that one ought to feed one's children, or that one has moral values—real values that exist out there in the world independent of the self.
The view is that the wrong-making features of actions are external, and they play a role in the development of essentially motivating moral sentiments that guide conduct.
[4][6] The view is vulnerable to a major concern for the ethical realist: projectivism may collapse into subjectivism or some variety of moral relativism.
Frank Ramsey (see his collected papers, edited by D. H. Mellor) and independently Bruno de Finetti, developed projectivist theories of probability in the early twentieth century.
This argument is moot, as the probability of the coin either landing on a heads or tails is 1, however, the observer is unable to accurately measure the input variables contributing to the output condition.
Thus, in the projectivist view, probability is a measure of the degree to which an observer believes in a given proposition of the outcome of an event.