Meditations on First Philosophy is a foundational text in modern Western philosophy, authored by the renowned philosopher René Descartes. This work is composed of six meditations, each building upon the previous, where Descartes embarks on a journey of philosophical inquiry and doubt.

In the first meditation, Descartes introduces the method of radical doubt, questioning the reliability of sensory experience, mathematical truths, and even the physical world's existence. This leads to the famous conclusion: Cogito, ergo sum (I think, therefore I am).

The second meditation explores the distinction between the mind, as a thinking, non-material substance, and the body, an extended, material one, introducing the concept of mind-body dualism.

In the third meditation, Descartes formulates his argument for the existence of God, positing that the idea of a perfect, infinite being must have originated from such a being, since a finite, imperfect being could not have conceived it independently.

The fourth meditation attributes human error to the misuse of free will, where judgments are made without sufficient understanding, rather than any flaw in God.

In the fifth meditation, Descartes presents the ontological argument for God's existence, asserting that the very idea of a perfect being necessarily includes existence.

Finally, the sixth meditation concludes that the external world exists, affirming the reality of material objects and the body, since a non-deceptive God would not allow clear and distinct perceptions to be false, although sensory experience can still be occasionally misleading.

This systematic method of doubt and reasoning establishes a secure foundation for scientific and philosophical knowledge, marking a significant shift towards individual reasoning and critical inquiry.