The study of biological classification (taxonomy or systematics) is indispensable to science and society. Even without training in biology, one can readily appreciate the value of names and descriptions of different kinds of organisms. Is this plant edible? Is that animal poisonous? What is that creature? Clearly, names are the keys to essential knowledge, and the means of communicating that information. Although one might expect that the task of discerning and naming living things is straightforward, in fact natural variation of plants and animals is extraordinarily complicated, and biological classification is based on sophisticated philosophy and complicated procedures. The theoretical and pragmatic issues of taxonomy are critically centered on what has come to be known as “the species problem”. If the species problem cannot be said to have been solved, at least the possible solutions are now apparent, as a result of prolonged empirical and philosophical inquiries. Sadly, the average biologist, let alone the average layman, has had little exposure to this intellectually stimulating issue.
In 1971, a brilliant semantic defence was advanced in a California criminal court case involving marihuana – a defence based on the possibility that there were “legal species” of marihuana plants. For the first time, courts in particular and society in general were squarely faced with the species problem and with interpreting the complicated subject matter of taxonomy.
{from Introduction, p. 3}