Among his philosophical works, Weiss is mainly known for his metaphysical writings, such as "Being and Other Realities". His other works include books and articles in epistemology and cosmology. He even published eleven volumes under the title "Philosophy in Process," detailing his continuing and sometimes daily reflections over the years 1955–1987. A recurring point in Weiss's philosophy is the claim that Being consists of a plurality of individuals that are unified by universality, which gives a structure to all there is, but that it is also irreducible in four distinct ways. During his prime, Weiss maintained a style of philosophy that was considered by many to be out-of-date. Weiss was opposed to various philosophies that were popular at the time, including that of the analytics, that of the logical positivists, and that of the Marxists. His was a philosophy which engaged in grand-scale philosophical system-building, much in the style of Kant, Hegel, or Peirce.