Wolff was not an original philosopher, but a modernizer and systematiser. Rather than reject scholastic school philosophy outright, as Thomasius had done, he modernized and systematised it (and philosophy as a whole). Systematizing philosophy meant integrating different ideas from the philosophical tradition -- Descartes's concept of substance, for instance, and Leibniz's theory of pre-established harmony. But while eclectic in this sense, unlike Thomasius's thought, Wolff's was anything but arbitrary. Rather, he combined those ingredients into a comprehensive system on the model of mathematics. Mathematics was, for Wolff, a systematic science operating by definition and syllogistic proof, and this was the method he strove to make applicable to philosophy. In philosophy, the method was cashed out in a combined analytic/synthetic manner. Definitions were arrived at analytically -- the analysis was to be of empirical matters and was to convey simple ideas through a process of clarification, abstraction, and analysis. These were then combined into definitions. The definitions were to function as ingredients in the syllogisms that returned, synthetically, to the empirical starting point, though it is presumably now understood why things are as they are, an understanding that was, for Wolff, the goal of philosophy.
The first philosophy text Wolff produced was his “German Logic” (Vernünfftige Gedancken von den Kräften des menschlichen Verstandes und ihrem richtigen Gebrauche in Erkenntnis der Wahrheit). Logic is of central importance to Wolff because it sets out the rules for thought, which is understanding's ability to forge connections, according to Wolff a uniquely human ability. All human beings have natural understanding, but by itself this is not sufficient. Logic or the “art of demonstration” serves to refine this natural capacity and functions, as well, as the condition of science. From the point of view of the enlightenment, it is instructive here that Wolff insisted, as Thomasius had before him, that book and memory learning is not the same as knowledge. That requires the use of the powers of the understanding, and above all, much practice in the art of thought. While innate, the powers of understanding have to be honed through practice/experience.
Wolff's second philosophical treatise, the “German Metaphysics” (Vernünfftige Gedancken von Gott, der Welt und der Seele des Menschen, auch allen Dingen überhaupt) appeared some seven years after the “German Logic”. Just as that had vindicated the discipline of logic against the early enlightenment attacks, so this vindicated the discipline of metaphysics, understood as the “science of the possible as possible.” After a brief introductory chapter identifying his Cartesian stance by linking existence to consciousness (we must exist because we are conscious of ourselves), the “German Metaphysics” treats ontology, empirical psychology, cosmology, rational psychology and natural theology. In the second chapter Wolff sets out the two (Leibnizian) principles governing his philosophical thought: the principle of contradiction (“something cannot both be and not be at the same time” §10, 6) and the principle of sufficient reason (“everything that is must have a sufficient reason why it is” §30, 17). These are significant not only from the point of view of Wolff's thought but also in light of the role they would play in early Kant-criticism. In the chapter on rational psychology (chapter 5), he defends the Leibnizian conception of pre-established harmony (§765, 478-9) and, in the final chapter on natural theology, he tells his readers that the world mirrors God's perfection (§1045, 648). These are aspects of Wolff's position with which the (pietist) Thomasians would take issue.
After the “German Metaphysics” appeared, Wolff published about a book a year dealing with and integrating into his system other central philosophical matters: ethics in 1720, politics in 1721, physics in 1723, teleology in 1724 and biology in 1724.
The ethics (Vernünfftige Gedancken von der Menschen Thun und Lassen, zu Berförderung ihrer Glückseligkeit) is composed of four parts, a theoretical part that treats the foundation of practical philosophy and three practical parts that present a doctrine of duties that human beings have to themselves, to God, and to others. Not surprisingly, given that Wolff believes the world to mirror God's perfection, the issue in the ethics is perfection as well and not, as with Thomasius, happiness (that is left for his politics). Moral perfection is the guideline by which we ought to choose between two (or more) equally possible actions. That is to say, when making a free choice we ought to consider whether the action “promotes the perfection of our inner and outer state” (§2, 5) and that means considering whether the state of the soul and the body accords with the prior state or contradicts it. The outcome has greater perfection to the extent that it contributes to the continued “natural human state and its harmonious preservation over time”(§2, 5). The natural human state Wolff envisions is the state of the soul in its manifold efforts to find truth, and everything has to be done to maximize that state (see “German Metaphysics” §152, 79). It so happens, that this is where happiness lies as well, and as Wolff indicates at the end of the ethics, it is incumbent upon human beings to ensure not only their own perfection/happiness, but to “contribute as much as possible to the happiness of others” (§767, 539).
In the “German Politics” (Vernünfftige Gedancken von dem gesellschaftlichen Leben der Menschen und insonderheit dem gemeinen Wesen), he proceeds to investigate the varieties of human societies and to specify how they ought to be set up so as to “promote the uninhibited progression to the common best” (§3, 3). A society must accord with the laws of nature, otherwise it cannot be considered a society, and accord with the laws of nature surely means perfection/happiness.
Wolff's Latin works appeared with equal regularity in the 1730, with the “Latin Logic” (Philosophia rationalis sive logica) beginning the series in 1728. In spite of their greater thoroughness, or perhaps because of it, they were not as widely read either in Germany or Europe as a whole. Whereas the German texts went through several reprints (14 for the Logic, 10 for the Metaphysics), the “Latin Logic” was only reprinted three times, and some of the other Latin texts perhaps twice. By the 1730s the German texts had established Wolff's influence and the Latin texts did little to change that. They will, accordingly, not be further considered in this context.