Margolis has a good premiss on the impact of habits of mind on our ability to perceive flaws in current theory and practice. However this information has been known to behavioral scientists for decades. Like Kuhn he has taken well known human traits and spun them into a "new" discovery. Old hat to people working in organizational change. The real annoyance with this book, apart from having paid for it, is that the main thesis is detailed in the first 29 pages and the next 200 pages give you more detail than you would ever wish on early chemistry and ptolemic astronomy. Get it from the library, if you must, my copy's going to the second hand book store for a refund to minimize expenses.

Why is it that at some periods of history it took hundreds of years to discover and important new law while all empirical data had long been available to logically infer the law or theory? This major question in the history and philosophy of science is being tackled by the barrier theory. The highly original work of Howard Margolis argues for the bold and strong thesis that revolutions in science mainly consist in surmounting a single conceptual barrier that prevents the emergence of a new theory. Margolis has previously published Patterns, Thinking and Cognition in which he argued that pattern recognition is all there is to cognition. In his defence of the barrier theory, he starts from the cognitive pattern he calls "habits of mind". These habits of minds govern our cognitive processes and are similar to what Polanyi called "tacit knowledge". Habits of mind guide our critical intuitions within a community and are therefore constitutive of a paradigm. A barrier is an entrenched habit of mind that can block a cognitive breakthrough in science. The conceptual distance between a prevailing view and a conflicting new proposal determines whether or not a paradigm shift within a scientific community takes place.
Margolis illustrates with historical examples how overcoming these barriers was critical for the emergence of new ideas in the seventeenth century. Even if one doubts the core idea of the barrier theory, Margolis' exposition on some of the major discoveries of the seventeenth and eighteenth centuries are convincing and truly original. In his account on the Copernican revolution Margolis shows that the critical barrier to overcome was not that of a stationary earth, as sometimes suggested, but the step to a heliocentric model with nested spheres. Using recently discovered notes of Copernicus on the Alphonsine tables, Margolis shows how logically simple it was to step from geocentric to heliocentric astronomy, but - as is typical with habits of minds - conceptually very difficult. Also his treatment of the emergence of probability theory is highly original. All intuitions for a probability theory were present for centuries, but the habit of mind was to perceive probability as a result of a bargaining process, like a fair price for the risks involved. The breakthrough of Pascal and Fermat was to attach a single quantifiable number to the concept of probability that was not considered to be countable. Once this missing concept was introduced of usefully attaching numbers to comparative values even if there is nothing immediately to count, a theory of probability could be established. Other case studies treated by Margolis are the overthrow of the phlogiston theory in the eighteenth century and the dispute between Hobbes and Boyle about the air pump. The conceptual barrier to view phlogiston as the negative for oxygen was removed by Cavendish's weight experiments with a mixture of inflammable air (hydrogen) and dephlogisticated air (oxygen) producing water when exploded. That was the birth of pneumatic chemistry in which gases suddenly became part of chemistry and which provided Lavoisier with arguments to abandon phlogiston. The dispute between Hobbes and Boyle on the air pump and the existence of vacuum is the subject of Shapin and Shaffer's seminal case study of constructivist analysis. Margolis is highly critical of their social constructivist approach and argues that they are simply wrong in their representation of Hobbes account. Instead of a constructivist interpretation, the dispute can be explained by the fact that the counterintuitive premise of living "at the bottom of an ocean of air" acted as a conceptual barrier for Hobbes understanding of the Boyle's experiments.

There can be some doubts about the nature of habits of minds acting as conceptual barriers in the process of scientific discovery. Margolis gives little evidence from experimental psychology or cognitive science to prove his case. But the analysis and case studies presented in the book are truly original and provide new insights for a theory on discovery. This work can therefore not be neglected in the study of scientific revolutions and philosophy of science.