Edward Conze is among the most important Western commentators on Buddhism. He is particularly important for his translation of the Prājñapāramitā-sūtra or The Perfect of Wisdom which exists in three versions of 18,000, 25,000, and 100,000 lines. The Prājñapāramitā-sūtra is important to the Mahāyāna tradition and especially the Mādhyamaka school. T.R.V. Murti has called the Mādhyamaka the "central" philosophy of Buddhism, and no doubt it played a very important role in the advance of Buddhism from its early Abhidharma period to the more inclusive Mahāyāna phase; but Conze's career and understanding of Buddhism is not limited to this particular tradition and he demonstrates his broad understanding in Buddhist Thought in India.
Early on, Conze virtually apologizes for writing Buddhist Thought in India citing Theodore Stcherbatsky's monumental work Buddhist Logic. According to Conze, Stcherbatsky has already covered Conze's topic in much greater detail and at much greater length than Conze can provide, but Conze is being overly modest here. While Stcherbatsky's work is brilliant and covers much of what is ing Buddhist Thought in India, the latter work provides a clear and concise explanation of topics that Stcherbatsky struggles to communicate. Stcherbatsky's work focuses mainly on the philosophy of three late period philosophers: Dignāga, Dharmakīrti, and Dharmottara. In contrast, Conze covers the entire sweep of Indian Buddhism.
Buddhist Thought in India is divided into three large parts covering Archaic Buddhism, Sthavira Buddhism, and Mahāyāna Buddhism. His treatments are evenhanded and respectful of each tradition. He describes both the historical developments that lead to each of these successive periods and explains the critical concepts that characterized them. According to Conze, Archaic Buddhism, i.e, the Buddhism of Buddha and his immediate successors, can be recognized by what is accepted by all (or most all) subsequent traditions, e.g., the impermanence of all things, the ubiquity of suffering, and the doctrine of no-self. His treatment of these and other important Buddhist concepts provide the reader with an excellent summary of the main tenets of Buddhism.
In the Sthavira phase of Buddhism, a number of disagreements arose over the interpretation of the main tenets. This led to a period of highly sophisticated philosophical debate in which the "abhidharma" or higher learning animated numerous Buddhists schools. Conze's treatment of these debates is good. Among them is the challenge by the heterodox Pudgalavādan school that asserted the existence of persons, virtually rejecting the doctrine of no-self. Conze also explores various views of impermanence and especially causation, but also the nature of space, nirvana, enlightened beings, and path to salvation.
It is in the section on Mahāyāna Buddhism that Conze really shows his expertise. He treats Mahāyāna's three main schools with clarity and precision: Mādhyamaka, Yogācāra, and the School of Logic. The first of these schools presents a stark break from the Sthavira tradition, leveling powerful criticisms of its philosophical positions and opening up Buddhism to a more popular following. In a more positive vein, the Yogācāra school advanced clear alternatives to the Sthavira tradition, sometimes disregarding the arguments of the Mādhyamikas. Finally, the School of Logic applied extraordinary scrutiny to the basic Buddhist concepts to bring Buddhism to its highest philosophical pitch. The work of the Logicians is far more completely explained by Stcherbatsky in his Buddhist Logic.
Among the larger arguments presented by Conze in this work is that when trying to understand Buddhism, one should not be fooled into thinking it is a purely rational philosophy that is compatible with modern science. According to Conze, Buddhism is unquestionably a religion with the goal of saving the world from suffering. It's empirical and metaphysical positions reach beyond the narrow scope of modern science and to leave out these elements misses its most important contribution to the world.