Just as we rarely question our ability to breathe, so we rarely question the habit of dividing human beings into two categories: females and males. At the birth of a child we ask almost automatically, ‘Is it a boy or a girl?’ The question carries important messages about both biological and cultural differences; the two categories seem natural and the differences between them obvious. However, much of our experience does not fit neatly into binary categories, and is better described as a continuum with indistinct boundaries. People relaxing at dusk experience the gradual change from day to night with no concern or precise word for the exact moment when day becomes night. Linguists travelling from village to village understand that there are no clear boundaries dividing one dialect or language from another. Berlin and Kay (1969) and Kay and McDaniel (1978) show that although basic colours have a universal biological basis, the variation across languages and individuals is so great that boundaries between colours can be identified only with fuzzy logic, a logic based on probabilities. In a study investigating how subjects distinguish between cups, bowls, mugs and vases, Labov (1973: 353) points out that although language is essentially categorical, ‘in the world of experience all boundaries show some degree of vagueness, and any formal system which is useful for semantic description must allow us to record, or even measure, this property’. Because language is discrete and biased towards dichotomy and clear boundaries, the scalar values and unclear boundaries of reality are sometimes difficult to recognize and to accept; we must continually remind ourselves that reality and 2language can conflict. The many real-world continua hidden by language suggest a question: is our automatic division of humans into female and male as justified as we think? Are the boundaries between them as clear as the words female and male suggest?