Duck, name collectively applied to numerous species of a family of waterfowl. Ducks differ from geese (see goose) and swans of the same family by their shorter necks and legs, and other anatomical features. They inhabit all continents except Antarctica, and some of the world’s islands. The legs of most ducks are placed far apart and towards the rear, making them clumsy walkers but efficient swimmers. The underplumage (down), which is buoyant and insulating, is kept water-resistant by frequent preening with oil from the uropygial, or preen, gland at the base of the tail feathers. Ducks, with the exception of mergansers, have spatulate bills lined with bony notches, or lamellae, for straining plant and animal matter from water.
Some island species have lost the power of flight, but most ducks of northern continents are highly migratory. In a few species, the sexes are alike in colour, but in most the males (drakes) are brighter and more boldly patterned.
II
COURTSHIP AND REPRODUCTION
Ducks have elaborate courtship displays, each unique to its species. Pair formation in most Northern-hemisphere ducks takes place in winter; hence—unlike most birds with seasonal plumage—males wear their bright plumage in winter, and briefly assume a female-like “eclipse” plumage during the summer. Nests of most species are on the ground, containing from 4 to 12 eggs, surrounded by down feathers plucked from the female’s breast and belly. Ducklings are able to swim and feed themselves soon after they hatch. Some species, such as the wood duck of North America, nest in holes in trees and will make use of artificial nest boxes. Their ducklings can jump from the nests without injury, and take to the water soon afterwards. They learn to fly in five to eight weeks.
III
MIGRATION
Distances covered by migrating ducks vary with the species. One Arctic duck, the spectacled eider, winters at sea off Alaska. Long-distance champion among European ducks is the garganey, which nests in most of northern Europe and winters in tropical Africa.
IV
TYPES OF DUCKS
Experts disagree about the classification of ducks into subfamilies and tribes, but the hundred or so species include a number of obvious groups. Most familiar are the dabbling or surface-feeding ducks, which include the mallard, ancestor of most domestic ducks. Members of this group live primarily on fresh water, where they glean plants and small aquatic animals from the surface or from the bottoms of shallow waters that they can reach without diving. The pochards, including the canvasback, nest by fresh water, but winter—often in very large flocks—on inland lakes and along the coasts; they feed by diving. Another group of diving ducks, including the goldeneyes and the bufflehead, nest in holes in trees. The mergansers are specialized for catching fish; the edges of their bills have sharp, tooth-like serrations for holding slippery prey. Of the European ducks the most marine are the eiders and scoters, which nest in the far north and winter predominantly at sea.
V
DOMESTIC DUCKS
All except one breed of domestic duck are derived from the mallard, originally tamed in Eurasia. The exception is the muscovy duck, a large species of the American tropics. Wild muscovies are mostly black, but the commonest domestic variety is white, with knobby, naked red skin around the face and bill. It and the turkey are the only domestic birds that originated in the Americas.
House
I
INTRODUCTION
House, a dwelling place for human habitation. Whether a crude hut or an elaborate mansion, and whatever its degree of intrinsic architectural interest, a house provides shelter and acts as a focal point for day-to-day living.
The physical characteristics of a house depend on climate and terrain, available building materials, technical skill, and such cultural determinants as the social status and economic resources of the owner or owners. In rural areas until modern times, people and animals were often housed together; today's houses frequently include storage, work, and guest areas, with several separate spaces for different activities. Houses can be wholly below ground level, dug out of the earth, or can be partly below and partly above the ground; most contemporary houses are built above ground (over cellars in cold climates). The primary structural materials employed are wood, earth, brick, and stone, with concrete and steel increasingly used, especially for city dwellings; many of these materials are also used in combination. Choice of material depends on prevalent style, individual taste, and availability. Depending on climate and available fuels, provisions may be made for heating. In modern industrialized areas, running water and interior toilets are common. Whatever its size and conveniences, a house both contains and stands for the basic human social unit.
II
HOUSES OF TRIBAL SOCIETIES
In tribal societies the house tends to consist of a single space, one room serving all activities. It is usually built directly against neighbouring structures and is often close to the tribal meetinghouse or religious building as well. The shape of such a house may be repeated through an entire village, creating fascinating patterns, as in the Dogon district of the Sudan or the settlements of Zambian herders. Such houses are often of simple geometric shapes—circular, with conical roofs, for example. Building materials are those available locally. If mud and clay are available, they are used to fill the spaces between pieces of wood or are made into bricks (usually sun-dried). Even huge reeds are used in the construction of dwellings, as by the marsh Arabs of southern Iraq. In rainy areas most tribal houses have interior hearths.
III
HOUSES OF THE ANCIENT WORLD
In ancient Egypt ordinary people dwelt in plain, mud-brick houses of rectangular plan. Excavations indicate that workers' houses had two to four rooms all on one floor and were densely packed into a gridlike pattern, with narrow alleys running between long rows of these quarters; the foremen had bigger houses. Throughout the Middle East much depended on the materials available. Where clay was found, beehive-shaped, single-room structures were common. Where stone but no timber was available, even the roofs were made of long strips of stone. These traditions continued well into modern times.
Except for the fairly elaborate chieftains' houses called “megarons”, Greek dwellings remained simple through Classical times. A passageway led from the street into an open court off which three or four rooms were set, the whole being fairly small in scale. Roman houses, as seen, for example, at Pompeii, also stood at the street's edge. Past a vestibule was an open space called the atrium, from which the sleeping rooms were reached; a colonnaded garden was often laid out behind the house. In ancient Rome most people lived in the equivalent of blocks of flats, three to five storeys high, each flat having three to six rooms; some were like tenements, others were elaborate. At ground level were rows of small shops. The rich had huge villas outside the cities that were composed of living quarters and pleasure pavilions.
IV
HOUSES OF MEDIEVAL EUROPE
This comparative sophistication in housing disappeared during the so-called Dark Ages in Europe. Although many people lived in castles and primitive manors, many also dwelt in simple, cramped, unsanitary dwellings huddled within the walls of towns and small cities. The countryside was unsafe, and agriculture and population both declined; the prosperous farms of Classical antiquity disappeared. Slowly, after ad 1000, conditions improved, first around the great monasteries and then in the expanding cities. The rise of a prosperous mercantile class resulted in the construction of large town houses and in due time country manors. Comparatively peaceful conditions brought some improvement in housing for farm serfs, but the living conditions of the poor town-dweller continued, on the whole, to be miserable. By the end of the Middle Ages the concept of the palace had evolved from the idea of the grand town house. These palaces were elaborate dwellings for high-ranking ecclesiastics, merchant princes, or ruling families; they might occupy a whole block and contain, in addition to ceremonial and private apartments, quarters for large numbers of retainers and various other people.
V
FROM THE RENAISSANCE TO THE 19TH CENTURY
The palace was perfected during the Renaissance and remains one of architecture's most enduring images, a dignified, large-scale city element that has been adapted and repeated ever since. Palaces were first built in Florence, Italy, and then throughout the Western world. In France the concept of the palace was combined with that of the late medieval castle to produce the French country château—the setting, with its gardens and fountains, of aristocratic life from the 16th century onwards. In England the lord's manor became the squire's hall, the centre of an estate that often included villages composed of the reasonably comfortable, thatched houses of local farmers. Meanwhile, in the towns and cities, some attempts were made to improve the housing of ordinary folk by building more or less uniform dwellings; on the whole, however, standards remained below those of Antiquity for a long time.
VI
19TH-CENTURY HOUSING
The Industrial Revolution brought some relief to the urban poor in the form of reasonably well-built rows of small houses for workers, especially in England, although these often degenerated into slums. The middle class in most Western countries, able to buy land and to build, rapidly acquired fairly comfortable large houses, the styles of which depended largely on local tradition. New means of transport, and the desire of the middle classes to own a plot of land, produced suburbs, where the majority of independently sited family houses are found today. The Industrial Revolution also spawned the dream of having one's own house irrespective of social or economic status. By the late 19th century the construction of houses had become a major architectural subject, studied by major architects. Books with drawings of both simple and elaborate houses were perennially popular, and domestic architecture was discussed in the new architectural journals as well. Houses became, for many, symbols of status. Cottages and bungalows, small one-storey dwellings each on its own plot of land, proliferated. Large ornate houses became fairly common, built in densely arranged groups in the older cities, standing alone in the newer towns and the suburbs. The popularity of distinctive styles of domestic architecture rose and waned. The technology for the supply of, for example, heat and water improved rapidly. Once the lift had been developed, tall apartment houses became an increasingly practical option, particularly in the United States after 1865. Workers' suburbs appeared and building speculators thrived. The role of the estate agent quickly became a fullblown profession, and houses began to change hands more frequently as families became more mobile.
VII
20TH-CENTURY HOUSING
Houses whose design broke with historical architectural styles were slow to be accepted. As early as 1889 the American architect Frank Lloyd Wright built a house embodying new concepts of spatial flow from one room to another. He and others, both in Europe and in the United States, soon moved towards a domestic architectural style of metric forms and simplified surfaces largely free of decoration. Contemporary changes in painting and sculpture were allied to this movement, and by the 1920s modern architecture, though by no means universally accepted, had arrived. Glass, steel, and concrete reinforced with steel gave architects many new design options, and by the mid-20th century the modern house was commonplace. Glass boxes, freely curving styles, and stark, austere geometric forms were all possible; but at the same time traditional styles persisted.
VIII
HOUSES OF THE FAR EAST
House types in India vary greatly according to region, climate, and local tradition. In villages, courtyard houses as well as simple, single-roomed dwellings are to be seen; in cities, densely populated tenements are found as well. Palaces abound in all areas; many are fortified, and some that are open to the land have multiple outbuildings such as pleasure pavilions. European influence is mostly limited to certain areas in the major cities. In China, the courtyard house, built of wood and having a tile roof, has persisted for many centuries. Walled in, it is a microcosm of Chinese social traditions. Rows of single-room dwellings, each with a tiny court or garden, are also found. At the other end of the scale are the imperial palace compounds, of which the Forbidden City in Beijing is the outstanding example. The various buildings of these compounds, laid out to form a vast, symmetrical complex, are a symbolic summary of the celestial claims of the emperors and the society they governed. In Japan, the traditional house is an elongated and somewhat rambling affair, made of wood and roofed with tile; if space is available, a garden, however small, is included. Good proportions in design and elegant simplicity of form are always evident. Western architectural influence has perhaps been greater in Japan than in the rest of South East Asia, although Japanese architects have themselves been in the forefront of the modern movement in architecture.
Mother Teresa
Mother Teresa of Calcutta (1910-1997), Albanian-born Roman Catholic nun, founder of the Missionaries of Charity, and Nobel laureate. Originally named Agnes Gonxha Bojaxhiu, she entered the Order of the Sisters of Our Lady of Loreto in Ireland at the age of 18. She trained in Dublin and Darjiling, before taking her religious vows in 1937. While serving as principal of a Roman Catholic high school in Calcutta (now Kolkata), she was moved by the presence of the sick and dying on the city's streets. In 1948 she was granted permission to leave her post at the convent and begin a ministry among the sick.
In 1950 Mother Teresa and her associates were approved within the archdiocese of Calcutta as the Missionaries of Charity. Later the order was recognized as a pontifical congregation under the jurisdiction of Rome. Members of the congregation take four vows on acceptance by the religious community. Required in addition to the three basic vows of poverty, chastity, and obedience is a fourth vow pledging service to the poor, whom Mother Teresa described as the embodiment of Christ.
In 1952 Mother Teresa opened the Nirmal Hriday (“Pure Heart”) Home for Dying Destitutes in Calcutta. Subsequently she extended her work to five continents. In recognition of her efforts she was awarded the Nobel Peace Prize in 1979. She was forced to scale down her activities in 1990 because of declining health, though she continued to work and travel, most notably in 1991 when she undertook a tour of her missions worldwide. Her increasing frailty became apparent when she resigned from running the Missionaries of Charity in March 1997, and she died on September 5 of that year. Mother Teresa's book, A Simple Path, was published in 1995.
Laws of Nature
I
Laws of Nature, pervasive general features of the world or descriptions of those features. Laws of nature are central to scientific investigation, in part because of the role they play in the prediction and explanation of natural phenomena. From antiquity people have considered why there should be regularities in nature. The status of laws has been a central topic in the history of theology because a deity provides a possible source of regularities and because of theological interest in miracles as violations of natural law. Laws of nature are also a central topic in the philosophy of science. There are two main philosophical questions about laws: the epistemological question asks how laws are discovered, while the metaphysical question asks what sort of thing they are.
II
THE EPISTEMOLOGICAL QUESTION
The epistemological question presents difficulties because scientists cannot deduce laws of nature from their data. For example, no matter how many ravens have been observed to be black, it cannot be deduced that all ravens are black: the possibility always remains that there is an unobserved raven that is not black. The logical gap between data and laws is even wider for scientific laws that concern entities, properties, and processes that are not just unobserved in fact but unobservable in principle. Scientists cannot actually observe that some light is a stream of photons, for example, much less that all light is like this. The evidence for such theoretical laws can thus only be indirect. Much of the philosophy of science is concerned with giving an account of the form such inferences take and of the justification that scientists can have for making them.
III
THE METAPHYSICAL QUESTION
At first glance, the metaphysical question about laws seems easier to answer. Difficult though it may be to state how scientists discover the laws of nature, it seems simple enough to say what sort of thing they are discovering. According to the straightforward answer to the metaphysical question, laws are simply universal patterns in nature or true universal generalizations, such as “all ravens are black”, or general mathematical relationships that science describes, such as Boyle’s law, which claims that the pressure of a given amount of gas at a constant temperature is inversely proportional to the volume it occupies, so that if the volume is reduced, the pressure is increased.
Such an answer is misleading, however, because not all true universal generalizations are laws. Even if by some extraordinary coincidence it turns out that every philosopher has been right-handed, it would not be a law that all philosophers are right-handed, though this universal generalization would be true. Similarly, even though it is presumably true that all the gold spheres that there will ever be will have a diameter of less than 100 miles (there being only a limited amount of gold in the world), this is not a law. Universal generalizations that would not be laws even if they were true are known by philosophers as “accidental generalizations”; on the other hand, generalizations that are laws if true are known as “law-like generalizations”. To understand what it is to be a law of nature requires explaining the difference between law-like and accidental generalizations. Philosophers have not found this an easy task.
Law-like statements appear to say more than accidental generalizations by describing not just how things are, but also how they would have been under different, counter-factual conditions. If it is a law that pressure is inversely proportional to volume, that is not just to state that the pressure goes up when the volume is decreased: even if the volume of a given sample of gas is kept the same, it is still the case that the pressure would have increased, had the volume been reduced. By contrast, even if it is true that all philosophers are right-handed, it is not the case that had a left-handed person taken up the subject, he or she would have suddenly become right-handed.
A second apparent difference between law-like and accidental statements is connected to the way laws are discovered. Only laws seem susceptible to inductive support. For example, if Boyle’s law is found to hold wherever it is tested, scientists may infer that it also holds in unobserved cases. By contrast, even if all the philosophers who were asked turned out to be right-handed, it would not be inferred that the same holds for the philosophers who had not been asked. The only way to be confident that all philosophers are right-handed would be to ask every one of them.
There are thus at least two apparent differences between laws and accidents: only laws have counter-factual content and only laws are susceptible to inductive support. It is not clear, however, that these two tests for lawfulness give the same answer for every generalization or that either gives the correct answer for every generalization. In addition, even if these tests were reliable, they only provide symptoms of law-likeness, rather then confirming directly what laws of nature are like. Philosophers have thus attempted to give deeper accounts of laws of nature and of what distinguishes them from accidental generalizations.
IV
DEFINING LAWS
Although there are many different and conflicting accounts of laws, they all fall into two groups. Almost all philosophers of science agree that some universal generalizations are not law-like. However, the accounts of the first group—sometimes known as “regularity views”—all maintain that law-like statements are simply a special class of universal generalizations, whereas the accounts of the second group afford law-like statements a different sort of content.
A
Regularity Views
There are three popular types of regularity view. According to the first, the “attitude” view, what distinguishes law-like from accidental generalizations is nothing in the generalizations themselves: it is instead a difference in our attitudes towards them. Thus, a supporter of the attitude view might say that law-like statements are those that scientists are willing to use for purposes of explanation or prediction. It is not that they are used in this way because they are laws; rather, they count as laws because they are used in this way.
According to the second account, known as the “projectible predicate” view, a generalization only counts as law-like if it contains the right sort of terms: for example, predicates such as “pressure” and “volume” can figure in laws, while perhaps “philosopher” or “right-handed” cannot. Proponents of the projectible predicate view then go on to consider what distinguishes “good” from “bad” predicates. Some proponents hold that good predicates correspond to natural kinds, whose members are fundamentally similar to each other, while bad predicates lump together dissimilar things.
The third type of regularity account is the “best system” view, in which laws of nature are those true generalizations that would feature in an ideal theory of the world. Such a theory could be constructed if everything was known and an optimal balance struck between the conflicting criteria of describing as much as possible while keeping things as simple as possible. Hence, many generalizations would fall within this theory, though many would be left out, since including them would incur too great a loss of simplicity for too small a gain in strength. The universal generalizations within the system are the laws; those without are the accidental generalizations.
B
Non-Regularity Views
Philosophers who reject the regularity view of laws also offer three different accounts. There is, first, the “property” view, according to which laws do not describe patterns of particular events in nature, but rather give relations between general properties. Thus, the generalization about philosophers being right-handed is not a law, because it is only a claim about particular philosophers; Boyle’s law, by contrast, is a law, because it describes a relationship between the general properties of pressure and volume.
A second account is the “necessity” view, according to which the essential difference between accidental and law-like statements is that whereas accidentals only describe what does happen, laws describe what in some sense must happen.
The final non-regularity account is the “capacities” view, in which laws are taken to be radically different from universal generalizations, describing instead the stable tendencies or capacities of physical objects. On the capacities view, laws do not describe patterns of actual behaviour of objects but rather the forces that underlie them, forces that combine in complex ways which preclude simple patterns. This view accounts for the fact that many laws of nature, such as Boyle’s law, describe only what happens under ideal conditions, when only a single set of forces is in operation. The aim of this view is to show how simple laws may reveal truths about a complex world.
