This book – being very concise and at the same time quite clear and quite dense, where nothing is missing, and nothing is overdone – is a good example of the type of scientific rigour appropriate for the history of philosophy. Chantal Jaquet, trained under the excellent instruction of André Lécrivain, then that of Jean-Marie Beyssade, had every means of carrying out this type of work effectively, and she completely succeeded at doing so. Its aim, precise and well defined, is, at root, to completely explain the possible definitions of both eternity and duration that we are given in the Ethics: What are their histories in Spinoza's first writings? What exactly do they mean? To what sort of beings does Spinoza apply the one or the other? What relations does Spinoza establish between the two forms of existence so defined? As for the accompanying method, it could be summarised in a single phrase: the texts, nothing but the texts, every text, with as little extrapolation as possible. Of course, such a method does not exclude philosophical reflection, much to the contrary: the author has a very sure knowledge of Spinozism, and the pertinence with which she uses it serves as its own evidence; but for this very reason, she only uses, at each step of her argument, what is absolutely indispensable for her aim. Without presupposing a comprehensive interpretation of the system in advance, without imposing anything in particular of it on us at the outset, she simply draws, with regard to the object of her work, a line of demarcation between plausible and implausible interpretations. This methodological asceticism, together with a modesty of intention, is precisely what guarantees the approach's effectiveness: the line is drawn in indelible writing. And its implications are enormous.

Just one example. The author's interpretation of the very subtle Spinozist definition of eternity – an interpretation that she opposes to mine, but no matter, since the consequences of it are the same – leads her to the conclusion that it is not improperly (as one often believes and as Gueroult himself seems sometimes to believe) but strictly and literally speaking that Spinoza attributes the property so defined not only to substance but also to infinite modes and, to a certain extent, finite modes, including the human intellect.