George Santayana was born in Madrid, Spain, on December 16, 1863, he was an influential philosopher, poet, and literary critic. His parents separated when he was very young, and he spent part of his childhood in Spain and part in Massachusetts, where he attended the Boston Latin School and Harvard College. He graduated from Harvard in 1886 then he studied in Germany for two years. He the latter part of his life, he returned to Harvard for his doctorate.

After completing his studies he joined the department of philosophy at Harvard, where he remained until 1912, when a legacy from his mother's estate allowed him to retire. He spent the period of World War I in England and later Paris, and finally settled in Rome. During World War II he lived in Rome in the convent of an order of English nuns. Santayana was the son of a Spanish father and an American mother. He thinks of the American mind as being more ingenuous than wise. American is the texture, Spanish is the structure of Santayana's mind. America impressed his spiritual outlook. But, successful as he was as an influential professor at Harvard, he never felt himself at ease there. The Spanish tradition corresponded more by far to his inclinations, and, although he did not care about authorities, he highly esteemed the soil of history, tradition or human institutions without which thought and imagination became trivial.

His early work can best be understood as that of a primarily poetic moral philosopher. His early works, The Sense of Beauty (1896) and The Life of Reason (5 vols., 1905-06), focus on the imaginative life of humanity, not on the underlying structures of reality or on humankind's mode of grasping reality. His later works, particularly Skepticism and Animal Faith (1923) and The Realms of Being (4 vols., 1927-40), are more concerned with a systematic development of the distinctions within nature and the different kinds of mental activities to which they relate.

Throughout his life, Santayana remained a naturalist and was concerned with the ideal factors in human existence and holding that everything ideal has a natural basis. For Santayana, human good consists of the harmonious development of humanity's impulses in conformity with the reflective ideational aspects of existence. He viewed religion as an imaginative creation of real value but devoid of absolute significance. Santayana's philosophical naturalism is systematized in his later, more directed work in terms of four major realms (his term) of being: essence, matter, spirit, and truth. Throughout his life Santayana also wrote poetry and literary criticism. His novel The Last Puritan (1935) received critical acclaim.

According to Santayana, essences neither necessitate nor explain thoughts, nor do they determine the ground of concrete existence. The seat and principle of genesis is matter, not essence, which, for its part, is explanatory of intuition, assures the form of apperception, elucidates existence, and helps the mind to grasp and to retain the character and identity of the changing existences. However, while the evolution of existing things changes their character at every moment, the essences, representing every moment of this change, remain in their logical identity. An essence is anything definite capable of appearing and being thought of: it is senseless to believe in it because belief involves the assumption of real existence.

Santayana as an anti-Idealist, maintained that not only does thought not constitute all of reality, but actually is not reality at all. Consciousness is like a fourth dimension, and its value consists in making something present to a subject. But what does consciousness make present? The essences of things. By the essences of things Santayana means the free constructions of the mind, symbols through which everybody expresses the universe as he interprets it. These essences are the kingdom of the spirit, and through them the spirit enriches itself. But essences, being merely a free construction of the spirit, do not tell us whether anything exists. How, then, may we be sure that there are in the extra-mental world things which correspond to these essences? Santayana maintains that we may never be certain of the existence of extra-mental things; reason cannot justify their existence, and hence Skepticism is inevitable.