Peter Munz had the unusual distinction of being taught by Wittgenstein (in Cambridge) and Popper (in Christchurch, New Zealand). He has also earned the distinction of being a truly quiet achiever in developing his ideas on several fronts, including the implications and applications of Popper's thought.

This book takes the debate over Popper's ideas past the point where it bogged down on falsification and the problem of induction. For some years after The Logic of Scientific Discovery appeared in 1959 critics offered two main lines of argument. First, they pointed out that no falsification by empirical evidence could be decisive (for example, due to the fallibility of observational techniques), therefore the falsification criterion of science was useless. Second, they claimed that scientific rationality depends on justification of theories and so Popper's theory of conjectural knowledge and his critique of inductive proof are twin daggers pointed at the heart of scientific rationality and a denial of the notion of scientific progress.

Popper and others replied that he had drawn attention to the limitations of falsification and his methodological strictures should be regarded as guidelines or conventions to maximise the exposure of theories to empirical tests. As to inductive proof, Popper argued that this was defective on purely logical grounds and so the rationality of science had better depend on something else which he attempted to provide with a theory of conjectural knowledge which shows how knowledge can grow without ever being proved certain or even probable.

Munz explains how Popper's writing since the early 1960s has increasingly treated matters of biology and evolution. This move supports the idea that rationality does not consist in the avoidance of errors but in the elimination of error and the correction of mistakes. In nature this occurs through the elimination of organisms and species by natural selection; in human affairs the primary method of error elimination can be the process of critical discussion. Munz points out that "mistakes" of a certain kind are necessary for biological evolution. These are the mutations that provide variations (new cards) beyond the range provided by the recombination of genes (shuffling the deck). Most of these "mistakes" are not helpful for the organism but some are advantageous. Desirable "mistakes" are thus analogous to the successful products of inventors, scientists and artists. We need these mistakes because if all sociocultural objects, ideas, rituals, procedures and traditions were reproduced faultlessly, the system would be closed, with no variation, no novelty and no possibility for change and progress.

Munz contends that a healthy culture will encourage experimentation and exploration at the risk of many false starts and dead ends. At the same time high standards of criticism will be maintained, though as Bartley has pointed out, criticism needs to be optimal, not too strict or hasty. To maintain this precarious balance a theory of criticism is required that focuses on objects or ideas and not on the personality or motives of the artist. In addition, an advance in cultural evolution is also needed permitting people to communicate with one another despite major and perhaps even fundamental differences in their respective belief systems. For most of recorded history, Munz suggests the basis of social and cultural bonding has been shared belief systems that are exempt from criticism. "Where knowledge is used a social bond, people cannot afford the luxury of exposing it to criticism, lest their co-operation be endangered or cease".

But now, in certain places, a threshold has been crossed: some people; "...have managed to establish societies which are not dependent on the purity of any given cultural strain and which are bonded by criteria other than the adherence to any particular belief system and its rituals."

The essential feature of such a society is that some aspects of its evolution can be regulated by critical discussion in a way that was previously not possible. However if this does not happen there may instead be further fragmentation, with the proliferation of self-contained and exclusive sub-cultures. To a very large extent this has happened in academic life and even within disciplines such as philosophy which have fragmented into communities which ignore each other's work.

Munz sees the tendency towards closed systems as a counterpart to sociological theories of knowledge whose defence of relativism expresses frustration with the failure of positivism and "mirror" theories of knowledge (as Munz calls them.) Mirror theories portray the mind as an inert vessel, or perhaps an induction machine, which accumulates knowledge as a result of passive exposure to the outside world. The extreme form of the mirror theory occurs in Wittgenstein's Tractatus with its "picture" theory of language in which all valid, meaningful and justified sentences mirror some extra-linguistic fact.

The classical alternative to the mirror theory of knowledge is the "lamp" theory, that the outside world is endowed with qualities projected upon it by the linguistic framework of the observer. This is essentially the view of Kuhn and Rorty, but Munz argues that both the mirror and lamp theories of knowledge contain the same structural error, namely the assumption that some authority is required to provide a grounding for indubitably justified beliefs. Munz wrote "After establishing that knowledge cannot be a relationship because it is not like 'mirroring', Rorty argues that it must be justified by something else. For Rorty, knowledge is not knowledge unless it is justified... In Rorty's view, the great divide in philosophy is between the upholders of mirror philosophy and the believers in the authority of speech communities. As against this, I would argue that the great divide is between justificationists of all persuasions and Popperians, who believe that we can have knowledge but that no knowledge can ever be justified."

Evolutionary epistemology, Munz contends, provides a way out of the impasse created by true belief theories of knowledge, whether of the mirror or lamp variety. Instead of falling back on justification, he advocates the employment of criticism leading to selection and tentative critical preference. But any shift from traditional theories of knowledge to an evolutionary epistemology requires theories of criticism to replace theories of justification. This Popper's decisive break with the philosophical mainstream.