Ernest Sosa (/ˈsoʊsə/; Spanish: [ˈsosa]; born June 17, 1940) is an American philosopher primarily interested in epistemology. Following a lengthy tenure at Brown University, since 2007 he has been Board of Governors Professor of Philosophy at Rutgers University.

Born in Cárdenas, Cuba, on June 17, 1940, Sosa earned his BA and MA from the University of Miami and his PhD from the University of Pittsburgh in 1964. His dissertation was supervised by Nicholas Rescher.

He joined the Rutgers faculty in 2007, having taught at Brown University since 1964. While full-time at Brown, he was also a distinguished visiting professor at Rutgers every spring from 1998 to 2006. Sosa has been described as "one of the most important epistemologists of the last half-century."

Sosa is a past president of the American Philosophical Association and a Fellow of the American Academy of Arts & Sciences. He edits the philosophical journals Noûs and Philosophy and Phenomenological Research. In 2005 he delivered the John Locke Lectures at Oxford, which formed the basis of his 2007 book.

Sosa received the 2010 Nicholas Rescher Prize for contributions to systematic philosophy, conferred by the University of Pittsburgh biennially. His son, David Sosa, is a professor and chair of the philosophy department at the University of Texas, Austin, and also specializes in epistemology.

In addition to epistemology, Sosa has also written on metaphysics, modern philosophy and philosophy of mind. In his books Knowledge in Perspective (1991) and A Virtue Epistemology (2007), he defends a form of virtue epistemology called "virtue perspectivism", which distinguishes animal knowledge from reflective knowledge.

"Contemporary virtue epistemology, conceived as such and as a distinctive movement within epistemology, began with Ernest Sosa’s work in the early 1980s." Virtue epistemology is characterized by two features: against W. V. O. Quine, it views "epistemology as a normative discipline" and "intellectual agents and communities as the primary focus of epistemic evaluation, with a focus on the intellectual virtues and vices embodied in and expressed by these agents and communities."

Absolutism and Its "explosion"
In "Existential Relativity," Sosa considers theories of composition. He calls ordinary theories of composition absolutism, which has objects as existing absolutely when compositional conditions are fulfilled in the object. Objects exist when certain stuff is arranged in a certain way. Absolutism leads to what Sosa calls an "explosion" of entities, in that an indeterminate number overlap at a location and any change destroys and creates an indeterminate number of others.