After mother’s milk or a manufactured equivalent, the first food that humans usually eat is pureed. Food that has been mechanically ground or pounded is convenient to learn on and it doesn’t require teeth, something we definitely lack at a young age. In former times, when oral hygiene was not part of one’s daily rituals, it was not uncommon for people to lose the majority of their teeth in early adulthood. For these people, food at the end of their lives was not much different than that at the beginning—pureed.
A few hundred years ago, all types of dishes were served as purees. Today, other than purée de pommes de terre—mashed potatoes—purees are rarely seen on the average dinner table. The exception in France is high-end restaurants where purees are more likely to included on the menu, but often as decoration rather than as a principal side dish.
In medieval times, purees were prepared from meats as well as vegetables. Today, most purees are prepared from just vegetables; which makes sense since today we eat purees for the flavor and mouth feel, not because we lack the dentures required to chew morsels of food.
In olden days, cooks were limited to using either a tamis (sieve) or a mortier et pilon (mortar and pestle) to puree foods. In the 19th century, the moulin de légumes (food mill) was added to the batterie de cuisine (kitchen utensils) available for the cook to use when preparing purees. The modern cook in an electrified kitchen now has the mixer or blender (stand blender); mixeur, batteur, or mini-mixer (stick or immersion blender); and robot de cuisine or just robot [see note below] (food processor) to simplify the process of preparing purees.
One advantage to purees is that the raw materials used in the preparation may not need to be in as good of a condition or as well formed as those where the same material is served whole or in large pieces. When preparing a puree, it is easy to cut out and discard any spoiled or damaged portions of the raw ingredient.
The consistency of a puree may vary from thin to thick. Generally, purees intended as a side dish or garnish are kept thick. Those meant to be eaten as a soup are thinner. (Soups with the word puree in their title, such as purée de céleri, tend to be a product of the late 19th-, early 20th-century. However, many soups are made today using the same processes as those used for making purees intended as side dishes, but they are not called purees on the menu.)
Raw materials used in purees which are too watery to produce a thick puree often have a complementary thickening ingredient added to increase their consistency. Typically, starchy vegetables, such as potatoes, cereals, such as rice, or thick sauces, such as béchamel, are added to thicken the puree.
If purees are dishes you avoid because there’s nothing to sink you teeth into, I strongly suggest giving one or two a try. Purees easily make up in taste what they lack in texture.
Note: I have not found a standardized word for food processor in France. I often see it referred to as a robot coupe, which is a brand of food processor. I have also been with chefs that refer to it as a mixer. The term used above is from the Harper-Collins French-English dictionary. Conversely, I have often seen the term mixer wrongly translated as a stand mixer by translators interpreting French recipes in English.