Reality is the conjectured state of things as they actually exist, rather than as they may appear or might be imagined. In a wider definition, reality includes everything that is and has been, whether or not it is observable or comprehensible. A still more broad definition includes everything that has existed, exists, or will exist.Philosophers, mathematicians, and other ancient and modern thinkers, such as Aristotle, Plato, Frege, Wittgenstein, and Russell, have made a distinction between thought corresponding to reality, coherent abstractions (thoughts of things that are imaginable but not real), and that which cannot even be rationally thought. By contrast existence is often restricted solely to that which has physical existence or has a direct basis in it in the way that thoughts do in the brain.Reality is often contrasted with what is imaginary, delusional, (only) in the mind, dreams, what is false, what is fictional, or what is abstract. At the same time, what is abstract plays a role both in everyday life and in academic research. For instance, causality, virtue, life and distributive justice are abstract concepts that can be difficult to define, but they are only rarely equalled with pure delusions. Both the existence and reality of abstractions is in dispute: one extreme position regard them as mere words, another position regard them as higher truths than less abstract concepts. This disagreement is the basis of the philosophical Problem of universals.The truth refers to what is real, while falsity refers to what is not. Fictions are considered not real.