Everytime you prepare a grocery list which separates the items into categories (such as "produce," "dairy," "meats," "frozen food," and "packaged goods") you are making a classification. For example, the term "produce' is a generic (or general) term which stands for many types or instances of something. Thus, under the term produce, you could make a further division into "fruits" and "vegetables." The words "produce," "fruits," and "vegetables" represent certain qualities by which you can sort individual items into these categories and not others. For, the fact that there is such a word as "produce" means that there are also food items that do not belong in that category. Thus, a classification enables us to simplify and specify--and ultimately define what we intend for something to mean. It also enables us to generalize--to identify relationships among things at increasingly higher levels of abstraction.
Some classifications seem obvious, such as grocery lists, sorting the silverware into a silverware holder, designating an "inbox" and an "outbox." Other classifications, however, allow us to discover and make new relationships among things. An example is the euglena, a single-celled organism which has properties of both plants and animals. The euglena is green and photosynthesizes its food from sunlight, as plants do. Yet it also possesses cilia, a tail-like structure, which enables it to self-propel (self-propulsion is a characteristic of the animal kingdom.) For many years, the euglena was classified as a plant, ignoring its animal-like characteristics. Eventually a new taxonomy was created, placing the euglena into the kingdom, Protista, which is neither plant nor animal--yet both. When the aggregate qualities of the euglena (greenness and self-propulsion) were finally taken together, it became clear to some that a new kingdom of living things was in order. Some classifications include all fungi and protozoans in this new kingdom. (Though others still classify such organisms in the Plant or Animal kingdoms, depending upon primary characteristics.) The kingdom Protista was recently added to biological classifications because organisms such as the euglena possess characteristics of both plants and animals. If there were no existing system for biological classification, there would have been no need to differentiate the euglena from plants and animals. Because of the worrk of earlier scientists (such as Linneaus, the eighteenth century Swedish botanist who eveloped the framework for the biolobical taxonomy still in use to day) later scientists were able to address the anomaly of the euglena and other such creatures.
Other scientists might begin to wonder about such anomalies--and question the chain of the evolution of life forms on the planet. Could members of the kingdom Protista mean that animals evolved from plants, or plants from animals? Or could we all have developed out of this kingdom, perhaps as relatives of fungi (such as mushrooms)? Classifications allow us to wonder about such patterns of relationships and to rearrange things into new categories to produce new relationships.....