The Four Noble Truths taught by the Buddha in His first sermon to the 5 disciples form the basis on which is founded the system of philosophy. In fact the first three Truths expound the philosophy of the Buddha while the fourth,

The Noble Eightfold Path which is a code of Morality-cum-Philosophy serve as a means for the end.
The Four Noble Truths are :

1. Dukkha Sacca = Noble Truth of Suffering,

2. Samudaya Sacca = Noble Truth of Origin of Suffering,

3. Nirodha Sacca = Noble Truth of the Cessation of
Suffering,

4. Magga Sacca = Noble Truth of the Path leading to the Cessation of Suffering.

To come to a complete understanding of the fundamental concepts in the philosophy of the Buddha, emphasis is laid on the need for the realization of the Truth of Suffering.

The Four Noble Truths
From the Dhammacakkapavattana Sutta:


1.) "And this, monks, is the noble truth of stress (suffering): Birth is stressful, aging is stressful, death is stressful; sorrow, lamentation, pain, distress, and despair are stressful; association with the unbeloved is stressful, separation from the loved is stressful, not getting what is wanted is stressful. In short, the five aggregates of clinging/sustenance are stressful.

2.)"And this, monks, is the noble truth of the origination of stress: the craving that makes for further becoming -- accompanied by passion and delight, relishing now here and now there -- i.e., craving for sensual pleasure, craving for becoming, craving for non-becoming.

3.)"And this, monks is the noble truth of the cessation of stress: the remainderless fading and cessation, renunciation, relinquishment, release, and letting go of that very craving.

4.)"And this, monks, is the noble truth of the way of practice leading to the cessation of stress: precisely this Noble Eightfold Path -- right view, right intention, right speech, right action, right livelihood, right effort, right mindfulness, and right concentration."

The Noble Truth of Suffering.

The Buddha taught that birth, sickness, old age, death, not getting what we
desire (want) or getting what we do not desire (do not want) are suffering.

The Noble Truth of the Origin of Suffering.

The Buddha taught that the origin (cause) of suffering is craving (selfish desire).
He also said that this selfish desire is a result of ignorance.

The Noble Truth of the End of Suffering.

He taught that the end of suffering is the end of the craving
(selfishness). This also means the end of greed, hate and delusion.
This end is called Nibbana. It is the highest happiness and peace.

The Noble Truth of the Way Leading to the End of Suffering.

The Buddha taught that the way leading to the end of suffering is The Noble Eightfold Path. It consists of right understanding, right thought, right speech, right action, right livelihood, right effort, right mindfulness and right concentration.

The Buddha was like a doctor. He saw suffering in the world, discovered the cause of it, cured himself and taught others the way to cure themselves.