Plato, also through the perspective of his teacher Socrates in Book IV of the Republic, noted that individuals can experience opposing desires simultaneously, such as being tempted to commit a crime but also feeling averse to it.
He reasoned that opposing actions cannot be performed simultaneously by a single entity, much like the impossibility for a person to walk in two opposite directions at the same time with one body.
However, given that human can experience conflicting impulses, he concluded that this phenomenon cannot be attributed to a single aspect of something within them - in this case, the soul. Instead, he proposed that it must be comprised of multiple aspects.
Plato identified that the soul must have at least two aspects. He named those two aspects as ‘reason’ and ‘appetite’, and added the third aspect, 'spirit,' which he believed should ideally be aligned with ‘reason’ in a healthy psyche.
To illustrate these three aspects, Plato uses the metaphor of a chariot, as given in Part 1.
The soul is likened to a chariot in the sky, with the rational part depicted as the charioteer who leads and gives direction.
The appetitive part is represented by a winged, dark horse that blindly chases after whatever it finds desirable, while the spirited part is symbolized by a winged, white horse that embodies nobility and obedience.
Plato also associates the three aspects of the soul to different parts of human body.
‘Reason’, or logos, is at the head, the seat of thought. ‘Appetite’, or eros, is at the stomach, the source of desire, and ‘spirit’, or thymos, is at the heart, where courage and determination reside.
Every soul is composed of these three parts, which means every human has all three aspects of the soul within them.
And what kind of a person they end up being is dependent on how these three parts of the soul interact with one another.
To be precise, Plato explains that the behavior and character traits of a person are determined by which part of their soul is dominant. He gives the example of love to illustrate his point.
Depending on which part of the soul dominates, love can take on different forms.
The most immediate and natural type of love is bodily love, where sexual desire drives attraction towards another person.
Here, the dark horse is in control, and if left to its own devices, it will keep them grounded in the physical realm, and the love that prevails will be no more than just the love of the body.
However, if the charioteer firmly steers the white horse and they together manage to subdue the dark horse, the desire for the body can be transformed into higher form of love, the love of wisdom.
Thus, the original physical attraction towards the other person can be channeled into a shared desire for knowledge and education, allowing them to learn from each other.
While the dark horse can lead a person astray if left unchecked, it is still the driving force behind their desires.
Without it, the person would be unable to desire anything, which is also problematic. With proper direction, however, this energy can be redirected towards positive ends.
In the end, the dominant aspect of one’s soul, be it reason, spiritedness and nobler emotions, or mere desires, is what shapes their character and defines the type of person they become.