Book: Possibility and Necessity in Modern Philosophy

Overview
Nicola Abbagnano offers a systematic study of the modal concepts that shaped modern philosophy: possibility, necessity, and contingency. The book traces how these notions were reformulated after the medieval period and how they became central to metaphysical, epistemological, and theological debates among thinkers such as Descartes, Leibniz, and Kant. Abbagnano treats modality not as a mere technical adjunct but as a hinge that reveals deeper commitments about essence, existence, reason, and freedom.
The treatment is historical and conceptual, seeking to show continuity and rupture across the modern period. Emphasis falls on how each philosopher redefines the status of modal claims, what must be true, what can be true, and what happens to contingency when reason claims sovereignty.

Historical context and methodological stance
The narrative begins with the decline of scholastic modal schemes and the emergence of early modern rationalism and empiricism. Abbagnano situates modal reflection within shifting views about God, substance, and the reach of human reason, arguing that debates about possibility and necessity were often proxy debates about metaphysical foundations and scientific method.
Methodologically, Abbagnano combines close textual reading with conceptual clarification. He aims to expose implicit assumptions in modal reasoning and to disentangle logical form from ontological commitment, making room for a more precise vocabulary of modality that can serve both historical understanding and philosophical critique.

Descartes and the primacy of clear and distinct necessity
Descartes is presented as a turning point where necessity becomes bound to the clear and distinct ideas guaranteed by God. For Descartes, necessary truths are those that reason apprehends immediately and infallibly, while contingency remains tied to creation and the finite nature of creatures. Abbagnano highlights how Cartesian certainty turns modal status into a marker of epistemic access as much as ontological status.
At the same time, Descartes' reliance on divine guarantee introduces tensions: the distinction between metaphysical necessity and epistemic certainty blurs, and questions arise about whether modal claims are features of things themselves or of our cognitive relationship to them.

Leibniz: possible worlds, necessary truths, and contingency
Leibniz receives thorough attention for his elaborate account of possible worlds, the principle of sufficient reason, and the distinction between truths of reason and truths of fact. Abbagnano explains how Leibniz makes necessity a function of logical and metaphysical entailment: truths of reason are true in all possible worlds, while contingent truths obtain in the actual world because of God's choice.
Leibniz's framework clarifies how contingency can be intelligible without lapsing into randomness, yet Abbagnano also probes difficulties: the metaphysical status of possible worlds, the ontological cost of positing a plenitude of possibilities, and the extent to which necessity remains independent of divine volition.

Kant, critique, and the reorientation of modality
Kant is portrayed as redefining modality through the critical turn. Necessity becomes tied to the synthetic a priori structures that make experience possible, and the scope of legitimate modal claims is limited by the conditions of human cognition. Abbagnano stresses Kant's move to secure certain necessities for science while denying speculative metaphysics the same reach.
This reorientation reframes contingency as a feature of empirical reality that escapes the same kind of a priori necessity. Abbagnano draws out consequences for moral and philosophical thought, noting how Kant's account both restricts metaphysical pretensions and opens a new way of understanding the normative force of certain modal judgments.

Philosophical implications and legacy
The book concludes by reflecting on the ongoing importance of modal concepts for questions of freedom, determinism, and the status of metaphysical explanation. Abbagnano's analysis suggests that possibility is not merely the negation of necessity but an active category that shapes human understanding and action. Contingency, far from being mere accident, marks the domain where practical freedom and historical novelty occur.
Abbagnano's work invites continued scrutiny of the assumptions behind modal vocabularies and encourages a balanced view that recognizes both the power and the limits of claims about what must be, what may be, and what happens to be.