The most difficult philoso­phers riddles

Theophrastus is often considered the father of botany for his works on plants. The two of his most important books, Enquiry into Plants and On the Causes of Plants, constitute the most important contribution to botanical science during antiquity and the Middle Ages as well as the first systemization of the botanical world.

Aristotle was invited by Philip II of Macedon to become the tutor to his son Alexander in 343 BC. Aristotle was appointed as the head of the royal academy of Macedon and encouraged Alexander toward eastern conquest.

François-Marie Arouet known by his nom de plume Voltaire, was a French Enlightenment writer, historian and philosopher famous for his wit, his criticism of Christianity, especially the Catholic Church, and his advocacy of freedom of religion, freedom of speech, and separation of church and state. He wrote more than 20,000 letters and more than 2,000 books and pamphlets.

In 343 BC, Aristotle was invited by Philip II of Macedon to become the tutor to his son Alexander (after years called Alexander the Great).

As Socrates did not write philosophical texts, the knowledge of the man, his life, and his philosophy is entirely based on writings by his students and contemporaries.

Immanuel Kant was German philosopher Immanuel Kant (1724-1804) is considered the most influential thinker of the Enlightenment era and one of the greatest Western philosophers of all times.

The categorical imperative (German: kategorischer Imperativ) is the central philosophical concept in the deontological moral philosophy of Immanuel Kant. Introduced in Kant's 1785 Groundwork of the Metaphysics of Morals, it may be defined as a way of evaluating motivations for action.