It is an engaging and entertainingly written book, whose purpose is to show the extent of scientific progress in the Middle Ages, and to dispel some prevalent and persistent myths about the period. I can't find serious fault so far (I have reached the 'condemnations' of 1277). While it has no news for students of the period, being mostly taken from (generally reliable and authoritative) secondary sources, the subject desperately needs a popular audience, and Hannam has succeeded brilliantly
Yet it has attracted fierce criticism. Charles Freeman, author of The Closing of the Western Mind, attacked the book in an essay in New Humanist, arguing that it presents a distorted view of the medieval period.
God’s Philosophers is ... poorly structured, without aHannam replied, and Freeman followed with a further critique.
coherent argument and often misleading, either through making assertions for
which there is no, or contrary, evidence or by omitting evidence that would
weaken its case. The review that called it “a spirited jaunt” was spot on. It
catches the mood of serendipitous ramblings, anecdotes and asides that make it
an easy read but hardly a serious contribution to our understanding of medieval
and sixteenth century science. Its success is mystifying.
I won't attempt any serious analysis of these, except to note Freeman's frequent accusation of Hannam's 'sweeping assertions'. Generalisation is difficult to avoid when you are attempting to cover nearly a thousand years of intellectual history in 300 pages. So far, Hannam has avoided it very well. His main arguments is are from example. He gives many stories and accounts, all sourced, showing the extent of medieval innovation. Many of them are simply intended to debunk myth and prejudice (I was particularly struck by the revelation that the synthesis of hydrochloric, sulphuric and nitric acid first occurred in the West in the thirteenth century, and not earlier in the Middle East). The only hint of generalisation I have found so far is on page 105. Hannam writes:
The condemnations [of 1277 when 219 propositions were banned in Paris] andThe passage is not sourced, and Hannam does not explain clearly the logic for his assertion. It is one of at least three views which Hyman and Walsh summarise it as follows.
Thomas's Summa Theologiae had created a framework within which natural
philosophers could safely pursue their studies. The framework first defined
clear boundaries between natural philosophy and theology. This allowed the
philosophers to get on with the study of nature without being tempted to indulge
in illicit metaphysical speculation. Then the framework laid down the principle
that God had decreed the laws of nature but was not bound by them. Finally, it
stated that Aristotle was sometimes wrong [...] and if Aristotle could be wrong
about something that he regarded as completely certain, that threw his whole
philosophy into question. The way was clear for the natural philosophers of the
Middle Ages to move decisively beyond the achievements of the Greeks (God's
Philosophers p. 105).
Most scholars agree that these condemnations had a profound effect on theBut it is a recognised view for all that. So far there is very little of distortion or falsification. I recommend the book.
history of medieval thought, but they disagree as to the nature and significance
of that effect. The condemnations have been called  a brutal victory
Augustinianism over Aristotelianism, but Aristotle flourished in the schools
after as well as before. It has been said  that by freeing the later Middle Ages
from the domination of a rigid Averroistic Aristotelianism, the way was opened
for the development of natural science as the inquiry into nature rather than
the dogmatic reiteration of the Aristotelian corpus. But surely this exaggerates
the monolithic character of the acceptance of Aristotle even by masters such as
Siger of Brabant, and underestimates the continued influence of Aristotle and
Averroes on the development of natural science. A more general and widely
accepted view  is that with the Condemnation of 1277, the scholastic effeort to
inforporate and renovate philosophy came to an end. But this surely
underestimates the philosophical advances, especially the methodological ones,
of the later period.