Truth and the good: why do we do evil? / Socrates -- Being and non-being: what is real? / Parmenides of Elea -- Change, conflict and harmony: how does the cosmos work? / Heraclitus of Ephesus -- The good and the just: what is the source of truth? / Plato -- Life in accordance with nature: can it make us happy? / Epictetus of Hierapolis -- Knowledge and belief: can we know anything? / Sextus Empiricus -- God and man: what is evil? / St Augustine -- God's necessity: could God not exist? / St Anselm -- Knowledge, faith and the soul: is the world good? / St Thomas Aquinas -- What there is: do ideas exist? / William of Ockham -- God, the world and our minds: how can we achieve certainty? / René Descartes -- The nature of God: do we have free will? / Benedict Spinoza -- God and the world: why is there something rather than nothing? / Gottfried Wilhelm Leibniz -- Faith: why should we believe? / Blaise Pascal -- Reason, freedom and equality: what did God endow us with? / John Locke -- Perception and causality: what can we know? / David Hume -- Reason, necessity and morality: how is knowledge possible? / Immanuel Kant -- History and the absolute: progress without good and evil? / Georg Wilhelm Friedrich Hegel -- World, will and sex: should we commit suicide? / Arthur Schopenhauer -- God and faith: do we need the church? / Sören Aabye Kierkegaard -- The will to power: is there good and evil? / Friedrich Nietzsche -- Consciousness and evolution: what is the human spirit? / Henri Bergson -- The foundations of certainty: what can we know and how can we know it? / Edmund Husserl.