Leibniz's philosophy posed a thousand questions to his contemporaries. On the essentials: the notions of monad, force and matter, the union of the soul with its body, the problem of Evil – and on the validity of the solutions proposed by pre-established harmony. Hence the writing, in 1714, two years before his death, of two systematic abridgements of his philosophy, the famous Monadology and the exemplary Principles of Nature and Grace where Heidegger identifies the ideal formulation of the metaphysical question. Leibniz offers a deductive exposition of his system based on the principles which found contingency and phenomena... Around these two major texts are gathered polemical writings, letters, remarks, reflections, considerations, interviews, so many particular points of view on the whole.