This book is overwhelmingly impressive, enormously enjoyable and utterly unconvincing. Israel tells the intellectual history of the French Revolution, which for him is the only history of the French Revolution. For Israel, the Radical Enlightenment was "incontrovertibly the one 'big' cause of the French Revolution ... the sole fundamental cause" (p. 708). He delves into the debates of the philosophes and the revolutionaries and separates a radical, progressive Jacobinism from the proto-fascist populism of Robespierre.
It was, Israel claims, the Brissotin Jacobins who believed in liberty, freedom of the press and equality. The Robespierre Jacobins are generally regarded as the most 'leftist', but were in fact populist authoritarians. The Brissontin "were the first to envisage tackling economic inequality and attempting to create a fairer society by constitutional, legal, and nonviolent means, especially tax and inheritance laws combined with financial assistance for society's weakest" (p. 478). They were committed to "freedom of conscience and basic human rights" (p. 485). The nub of my problem with the book is that Israel keeps discovering that the best of enlightenment thought coincides exactly with a contemporary radical social democratic platform. The very terms that he uses to describe their politics are strikingly contemporary - 'basic human rights' rather than 'rights', and a focus on inheritance tax and financial assistance for 'society's weakest', which sounds like it's taken straight from Polly Toynbee. I don't question Israel's phenomenal knowledge of eighteenth century sources, but I am suspicious that he keeps finding them to accord so perfectly with a specific strand of twenty first century politics.
He writes very little about the motivations of individual actors beyond the ideas that they propounded, which is an interesting contrast to an earlier influential synopsis of the Enlightenment by Peter Gay, who was a Freudian historian. However, he does claim that Robespierre suffered "psychological sickness" (p. 546). That may well be true, but it is one-sided to identify psychological flaws only in those with whom you disagree.
One comment that stuck out for me was the claim that Babeuf was an advocate of 'social justice' (p. 595). It stuck out because the term 'social justice' is a trope of contemporary social democracy, implying the extension of formal equality before the law to claims about the rightfulness of social provision. It is not a term I associated with the Enlightenment or the French Revolution. I checked Google Ngram, which searches the entire corpus of scanned books to show the usage of words over time, and it confirmed that it is a twentieth century concept, its use spiking in the 1930s, 1960s and especially from the 1990s. The French term shows a similar trajectory; it was used around the time of the French Revolution, but only very rarely.
In the history of political ideas it's become hard to say anything political, because the field has become so pedantically antiquary. Academics unearth nuances of meaning that were important to twelfth century theologians, which is all very interesting and important, but they are often wary of drawing conclusions for today. They are reacting against the naive ahistoricism of earlier generations of scholars who treated historical ideas as resources to plunder to resolve modern disputes. Jonathan Israel breaks through the nit-pickiness of some current scholarship, but at the expense of repeating old mistakes. He seems to read enlightenment thinkers from 'his' side as simply modern social democrats.
Israel's command of his sources is terrific, and there are lots of good anecdotes. I like the story of Brissot calling for delegates to the National Assembly with the right intellectual level and the right principles, regardless of social class - but warning that big merchants should be regarded with suspicion, and bankers are worst of all; they "should be generally shunned and excluded from the legislature as an entirely antisocial group" (p. 156). I learned a lot from this monumental and important book, and I enjoyed reading every page. I don't agree with it, but I recommend you read it.