The principle that nature follows exact laws, so that what will happen in the future is a necessary consequence of the state of the world at any given moment in the past. This view, if fully adopted, implies that events which seem to occur by chance would be fully understood if more was known about them, and that apparently free thoughts and choices are explainable and in principle predictable in terms of neuroscience. In a looser sense, determinism refers to claims that mental freedom is much more restricted than is generally supposed. An immense philosophical literature has arisen in response to this challenge to the sense of humanity, most of it defending the freedom of a person's choices and the necessity that the individual be held responsible for them.