Philosophy:
* Philosophie politique (1854) - A work exploring political philosophy and the role of the state.
* Philosophie sociale (1858) - A treatise on social philosophy, analyzing societal structures and dynamics.
* La Logique et la Psychologie du Droit (1881) - An examination of the logic and psychology underlying legal systems.
* Le Monde et la Vie (1882) - A book addressing metaphysics and the nature of reality.
* De l'Origine du Droit (1885) - An investigation into the origins and evolution of law.
History:
* Histoire du peuple d'Israel (1856) - A historical account of the Israelite people.
* Histoire des Arabes (1861) - A history of the Arab civilization.
* Histoire de la littérature française (1872) - A history of French literature.
* Histoire des doctrines politiques (1883) - A history of political doctrines.
Journalism and Political Commentary:
* Le Figaro - Proal was a regular contributor to this prominent French newspaper, writing on politics, philosophy, and current affairs.
Other works:
* Le Sens Commun et la Raison (1868) - A defense of common sense and its role in human reasoning.
* Les Grandes Philosophies (1871) - A summary of major philosophical systems.
* Le Réalisme (1873) - A book advocating for a realist approach to philosophy.
* La Vie et l'Art (1886) - A work exploring the relationship between life and art.
Proal's writings were often controversial, as he was a strong advocate for individual liberty and a critic of socialistic and collectivist ideologies. He was also known for his sharp wit and his ability to engage in intellectual debates.
While many of his books are now out of print, his work continues to be studied by scholars of philosophy, history, and political thought.