Numbers play a central role in our lives. Numbers and number expressions arise early both in human history and in the individual development of children. Numerical notations existed long before the invention of script, and archaeological evidence suggests that at least 30,000 years ago our ancestors used notches as primitive representations for collections of things. Newborns in their first week of life can already distinguish two from three objects, and children start using number words and engage in counting games as early as two years of age. In our everyday life we use numbers in a wide range of different contexts; we employ them not only for counting, but also for telling the time, on price tags, for football scores, to rank runners in a marathon, for bus lines, as telephone numbers, in lotteries, and so on. And in one way or the other, numbers play a role in the spiritual contexts of most cultures. They are employed in fortune-telling, and in many cultures certain numbers, say 13, are associated with bad luck, or certain kinds of number assignments fall under taboo restrictions, for instance, it might be considered imprudent to count people or to count your own children.

What makes numbers such a fascinating topic? I think the fascination that numbers have for us arises from their great significance as reasoning devices, as powerful and highly flexible mental tools.