"Thinking hurts" — this is how the German philosopher Georg Simmel is said to have consoled his students. The Jewish philosopher Martin Buber (1878-1965) would give this ironic remark of his teacher an ethical twist by noting that "thinking" can also hurt others.

For in our encounter with our fellow human beings we often tend to allow established categories of thought to determine how we relate and perceive them. In doing so, Buber held, they in effect become objects of thought, an "It", rather than indivuals whose existential reality is impervious to the markers that thought constructs.

To be sure, these markers — concepts and categories — may be intrinsically benign and essential to navigating the multiple by-ways of life. We need them to recognise others and position them in the sociological landscape of everyday life: the other may be a physician, an electrician, a priest, a rabbi; elderly, young, tall, slim. But these markers, as indispensable as they may be, cannot comprehend that distinctive existential reality of the other.