The Enlightenment is one of the formative periods of Western history, yet more than 300 years after it began, it remains controversial. It is often seen as the fountainhead of modern values such as human rights, religious toleration, freedom of thought, scientific thought as an exemplary form of reasoning, and rationality and evidence-based argument. Others accuse the Enlightenment of putting forward a scientific rationality which ignores the complexity and variety of human beings, propagates shallow atheism, and aims to subjugate nature to so-called technical progress.

Answering the question 'what is Enlightenment?' Kant famously urged men and women above all to 'have the courage to use your own understanding'. Robertson shows how the thinkers of the Enlightenment did just that, seeking a rounded understanding of humanity in which reason was balanced with emotion and sensibility. His book goes behind the controversies about the Enlightenment to return to its original texts and to show that above all it sought to increase human happiness in this world by promoting scientific inquiry and reasoned argument. His book overturns many received opinions - for example, that enlightenment necessarily implied hostility to religion (though it did challenge the authority traditionally assumed by the Churches). It is a master-class in 'big picture' history, about one of the foundational epochs of modern times.