Descartes’ Dualism

Descartes investigated the connection between the mind and body, and how the two interact. His main influences for dualism were theology and physics. The theory on the dualism of mind and body is Descartes’ signature doctrine and permeates other theories he advanced. Known as Cartesian dualism, his theory on the separation between the mind and the body went on to influence subsequent Western philosophies.

According to Descartes two substances are really distinct when each of them can exist apart from the other. Thus Descartes reasoned that God is distinct from humans, and the body and mind of a human are also distinct from one another. He argued that the great differences between body and mind make the two always divisible. But that the mind was utterly indivisible, because “when I consider the mind, or myself in so far as I am merely a thinking thing, I am unable to distinguish any part within myself; I understand myself to be something quite single and complete.”

Descartes’ dualism of mind and matter implied a concept of human beings. A human was according to Descartes a composite entity of mind and body. Descartes gave priority to the mind and argued that the mind could exist without the body, but the body could not exist without the mind.

Cartesian Doubts


Doubting the senses
. Descartes begins by pointing out that our senses are unreliable
. So, we can doubt that what our senses tell us is accurate and so they cannot be the foundation


Doubting the physical world
I have seen tables in my dreams, I could be dreaming of it.
Evil genius is determined to deceive you into thinking that there is a physical world when there isn’t one

Doubting Mathematics
Descartes thinks that he can imagine a scenario in which 1 + 1 does not equal 2
evil genius is tricking me into thinking that 1+1=2



Avicenna (also Ibn Sīnā or Abu Ali Sina; c. 980 – June 1037) was a Persian polymath who is regarded as one of the most significant physicians, astronomers, thinkers and writers of the Islamic Golden Age. He has been described as the father of early modern medicine.

Avicenna wrote his famous “Floating Man” – literally falling man – thought experiment to demonstrate human self-awareness and the substantiality and immateriality of the soul. Because it is conceivable that a person, suspended in air while cut off from sense experience, would still be capable of determining his own existence, the thought experiment points to the conclusions that the soul is a perfection, independent of the body, and an immaterial substance. The knowledge that “I am” is the core of a human being: the soul exists and is self-aware. The body is unnecessary; in relation to it, the soul is its perfection. In itself, the soul is an immaterial substance.

Avicenna made an argument for the existence of God which would be known as the “Proof of the Truthful“. Avicenna argued that there must be a “necessary existent“, an entity that cannot not exist and through a series of argument.

    • Contingent: has a reason for its being
    • Necessary: has no reason for its being
    • God = the necessary being
    • Suppose there were no necessary being
    • Everything, including the current state of the world, YOU, would be contingent
    • There would be an infinite series:
    • You <- father <- his father <- his father <- ….
    • But then the conditions for YOU existence would never be satisfied
    • So, there is a necessary being, God

Boethius – Consolation of Philosophy

Anicius Manlius Severinus Boëthius, commonly called Boethius (c. 477–524 AD), was a Roman senator, consul, magister officiorum, and philosopher of the early 6th century.

In 522, the same year his two sons were appointed joint consuls. In 523 Boethius fell from power. After a period of imprisonment in Pavia for what was deemed a treasonable offence, he was executed in 524.

Boethius writes the book as a conversation between himself and Lady Philosophy. Lady Philosophy consoles Boethius by discussing the transitory nature of fame and wealth (“no man can ever truly be secure until he has been forsaken by Fortune”), and the ultimate superiority of things of the mind, which she calls the “one true good”. She contends that happiness comes from within, and that virtue is all that one truly has, because it is not imperilled by the vicissitudes of fortune.

Boethius told us: If you are in possession of yourself you will possess something you would never wish to lose and something Fortune could never take away.

Augustine of Hippo


Saint Augustine of Hippo 13 November 354 – 28 August 430)was a Roman African, early Christian theologian and philosopher from Numidia whose writings influenced the development of Western Christianity and Western philosophy.

Augustine saw the human being as a perfect unity of two substances: soul and body. Initially, the two elements were in perfect harmony. After the fall of humanity they are now experiencing dramatic combat between one another. They are two categorically different things. The body is a three-dimensional object, whereas the soul has no spatial dimensions. Soul is a kind of substance, participating in reason, fit for ruling the body and the soul is superior to the body.

A will defiled by sin is not considered as “free” as it once was because it is bound by material things, which could be lost or be difficult to part with, resulting in unhappiness. Sin impairs free will, while grace restores it.


Augustine boldly wrote a letter urging the emperor to set up a new law against slave traders and was very much concerned about the sale of children. Augustine believed that slavery did more harm to the slave owner than the enslaved person himself.

 Augustine, who believed Jewish people would be converted to Christianity at “the end of time”, argued that God had allowed them to survive their dispersion as a warning to Christians; as such, he argued, they should be permitted to dwell in Christian lands.

Medieval Philosophy

Medieval philosophy is the philosophy in the era now known as medieval or the Middle Ages, the period roughly extending from the fall of the Western Roman Empire in the 5th century A.D. to the Renaissance in the 16th century.

Medieval philosophy is characteristically theological. All the main branches of philosophy today were a part of Medieval philosophy. 

The principles that underlie all their work are:
    • The use of logic, dialectic, and analysis to discover the truth, known as ratio;
    • Respect for the insights of ancient philosophers, in particular Aristotle, and deference to their authority;
    • The obligation to co-ordinate the insights of philosophy with theological teaching and revelation.

Plato’s Theory of Ideas or Forms

Plato thinks that there is the goodness itself in the world of Forms.

The theory of Forms (or theory of Ideas) typically refers to the belief that the material world as it seems to us is not the real world, but only an “image” or “copy” of the real world.

Plato applies this concept to all of material things.

According to Plato, there may be a tree itself in somewhere.

Trees that we can see in our lives share the property of the Form of the tree itself.

The reason why trees are trees is that they participate in the Form of the tree itself.

The reason why other things are not trees is that they don’t participate in the Form of the tree itself.


Plato’s “World of Forms”

Not only exists the world that we live our lives but also the world of Forms (or Ideas) exists.

This is what Plato actually wanted to say.

The world of Forms is the true and real world. The world that we live is the world of shadows.

The world of Forms is the original world. The world that we live is the model world.

Therefore according to Plato, we must not cling to the world that we live now.

We must seek the world of Forms.

This is the way that we do philosophy.

Zeno of Elea

Zeno of Elea (c. 490 – c. 430 BC) was a pre-Socratic Greek philosopher of Magna Graecia and a member of the Eleatic School founded by Parmenides. Aristotle called him the inventor of the dialectic.

Zeno is also regarded as the first philosopher who dealt with the earliest attestable accounts of mathematical infinity.

Zeno’s Dichotomy paradox

Suppose Homer wishes to walk to the end of a path. Before he can get there, he must get halfway there. Before he can get halfway there, he must get a quarter of the way there. Before traveling a quarter, he must travel one-eighth; before an eighth, one-sixteenth; and so on.

This description requires one to complete an infinite number of tasks, which Zeno maintains is an impossibility.