Metaphors make speech and text enjoyable. A text can become terribly dry and prosy, if the metaphors are removed. However, metaphors do not only have an aesthetic value: metaphors are often necessary in order to grasp phenomena that still lack established concepts, or that are too complicated or abstract (for a particular purpose or a particular audience) to be explained in literal words. When a phenomenon is simplified by using a metaphor, it, however, usually means emphasizing one aspect and obscuring others. A metaphor may help the observer to see a phenomenon from one perspective, which means not seeing it from another perspective. Isn't it true that life is a theatre! But used in the wrong context, the metaphor might hurt. In times of pain and sorrow, life is no theatre.
In order to understand or grasp something new, unknown, complicated or abstract, we borrow models from things that are already known or which are more concrete. When the space ship was new, it was apprehended as a ship for journeys in space, like the air ship had been a ship for journeys in the air. Today computer viruses are imagined as viruses which infect. Perhaps in the future, organic viruses will be imagined as software, that one should protect one self from with the help of (organic) anti-virus programmes.
If we consider the notion of ship, we may say that this notion has acquired a wider sense. However, as for the notion of virus, it is obvious that, in spite of the common term, we are dealing with two entirely different notions, which are coupled with each other by an analogy.
Sometimes a distinction is made between metaphor and simile as well as between proper metaphor and on the other hand metonymy, synecdoche and irony. It is however not always clear whether a metaphor is a metaphor proper or not. I will here use the notion 'metaphor' in an inclusive sense. Still, it might be needed to give these concepts definitions. With metonymy I understand the replacement of a word with the name of a thing nearly associated: we say that we read Kafka, when we actually read some literature written by Kafka; we talk about the White House, when we refer to the President of the United States. With synecdoche, which sometimes is interpreted as a kind of metonymy, I understand the replacement of the name of referred thing with the name of a part of this thing: fifteen heads for fifteen persons, butter on the bread for welfare. Sometimes metonymies and synecdoche's are only shortenings, but they often say more or less than the proper word: they exemplify, dramatize or create desired fuzziness.
An expression may sometimes be interpreted as a metaphor proper as well as a metonymy. Lots of examples can be found in vulgar speech. - I will not mention any here. But a metaphor in a proper sense may also be used as a metonymy on another level. If we mention the Holy See, we thereby let the see, i.e. a chair, represent the entire papacy, but the chair itself is a metaphor. If we talk about the fall of the Berlin wall, we seldom talk about the concrete event of tearing down the wall. Instead, we use one detail, the destroying of the wall, as a synecdoche of a more comprehensive process. Additionally, the fall of the Berlin wall is a metaphor that figuratively describes the unification of Germany and the whole Europe.
After the retreat of the Finnish president Urho Kekkonen, a book was published with the title Tamminiemen pesänjakajat. Here pesänjakajat is a metaphor proper, while Tamminiemi (the home of the former president) is a metonymy. As a whole the notion is, however, clearly metaphoric. The Paris-Bonn axis used to be mentioned in political texts. Here the axis is a metaphor, perhaps a dead one. But even Paris and Bonn are metaphors, or parts of a metaphor, and metonymies as well. As metonymies they represent the respective governments or central administrations. It is, however, not self-evident that the name of a capital is used for the government of a country. At least outside Italy, "Rome" usually stands for the Pope and the Catholic Church. Similarly, outside Belgium, "Brussels" stands for the European Union and its various bodies, of which not all are located in Brussels.
Lets move on to more scientific matters. A scientific text is supposed to use exact and well defined concepts. Accordingly, metaphors are banned. Still many exact scientific concepts are originally coined as metaphors. When the concepts have established themselves, they have become dead metaphors, that are not any more associated with the word in its literal sense. However, metaphors are not always as dead as they seem to be.
Take black holes as an example. A black hole is not a literal hole. Hardly any physicist imagine that it would be, but among laymen there are many, who imagine black holes by the model of literal holes. For physicists it does not make a big difference that black holes are called "black holes" and not for instance "cosmic implosions", but for laymen as well as for writers of science fiction, it might be a determining factor in the understanding of what a black hole is. We could add that the English word 'hole' has two (or more) meanings. How the word 'hole' is translated to other languages can further on influence conceptions about black holes. Still, the notion 'black hole' is, as a metaphor, an innocent one.
In physics it is not always obvious whether we are dealing with a metaphor or only an analogy when we use the same name for two entirely different but structurally similar things. Without the common form with more concrete things and phenomena, it would often be extremely difficult to get an idea of certain aspects of the physical world. Physics has borrowed lots of terms from other fields of knowledge and most of the terms are by no means chosen randomly. But physical notions have further been borrowed into other fields. Ironically, it is often so that neither humanists nor physicists have realized that we are here usually dealing with metaphors or, at its most, analogies. There is no point in being against the (postmodernist) use of scientific metaphors and analogies, as long as it is clear that the metaphors are just metaphors and the analogies just analogies. If a physical appellation is used in a transferred sense in another field, the experience from physics may help us to understand a phenomenon which does not belong to the world of physics, but physics may have borrowed the same term from a non-physical phenomenon that is in some way similar.
In the didactic of physics, dead metaphors may be brought back into life for purely pedagogical reasons. When a pupil or a student is learning something new, he will understand the notion as a metaphor. When he has learned to know the phenomenon, the metaphor will become a dead metaphor for him too. The teacher may even use parables and metaphors that are not suggested by the name of the phenomenon. When the physics teacher compares the force between positively and negatively charged particles with the attraction between a man and a woman, he is thereby helping the pupils to understand the physical phenomenon, but in the same time he gives them a model for the sexual orientation of (normal) human beings.
One dominant figure of speech or model of thought that has been borrowed from natural science to economics is the "natural selection". Darwin's theory of the evolution of species helps us, transferred to another level, to get an idea about the mechanisms of the free market economy. (Whether the idea is right or wrong is an other topic.) Nevertheless, Darwin himself is supposed to have taken inspiration for his theory from the liberal economical theories of his time. It is not always easy to tell which one came first, the egg or the hen.
One could claim that the Darwinist model helps us to understand the market economy, although it gives a wrong understanding. The Darwinist paradigm perhaps help us to misunderstand the market mechanisms, but also misunderstanding is a kind of understanding, although not it an exclusive sense. Whether a model gives a correct understanding might depend on how much of the model is taken from the one field to the other one. The image of particles helps us to understand elementary particles, as long as we don't apply the idea of solidity to the elementary particles.
In the humanities and, especially in history, living metaphors are used even in specialist literature. The phenomena that history gives an account of are so complex, that any interpretation demands simplifications. Simplify is just what metaphors do. Metaphors expose some aspect of a phenomenon, while they hide other aspects. Metaphors can, just for that reason, be used to interpret the past according to specific interests. Compared to metaphors used in natural science, metaphors used in historiography are not completely innocent.
In religion and politics metaphors are still more common and visible than in history. Religious people might not apprehend metaphors as metaphors, but religious language is difficult to imagine without metaphors. To be religious with necessity implicates to live by metaphors. The choice of images might also have an impact on the structure and rules of the community as well as on religious life. If, for instance, a priest is understood as a father it might be more difficult to accept female priests than if a priest is understood as an elder, as a shepherd or a minister. Whether God is a father, the Lord of Hosts or a hen that gathers her chicks under her wings has an impact on the relationship with God. The metaphors of religious language are innocent in the sense that the minister or at least the common religious person seldom create or choose a specific metaphor in order to convince people about something. In religion metaphors are given. The Lord remains "my shepherd", even if young urban people hardly know what a literal shepherd is.
Political metaphors, unlike religious metaphors, are often consciously chosen, in order to support certain interests. When Finland in the middle of the 90's was to decide whether to join the European Union or not, the discussion concentrated on whether there would be other trains, if we lost the current one, and in which class - first or second - Finland in that case would travel. To travel together with former communist East-European countries would not have been pleasant! The metaphor did not question whether it was desirable to get to "Brussels". (Here Brussels is also, of course, a metaphor or perhaps a metonymy.)
In the time of the Soviet Union Finland and Finnish politicians had to keep good relations with "Moscow". By using this metonymy, one could avoid specifying who exactly one wanted to please. - Perhaps "Moscow" even sometimes stood for the Finnish president Kekkonen! By using the Moscow metaphor one could also avoid telling who exactly had the power in the Soviet Union.
Recently the Finnish presidential election has been discussed using a game-terminology. Game is an old metaphor for politics and political acting and not remarkable in itself. When the election has been compared to a game of cards or horse racing it has been obvious that the game is a metaphoric one, but when the word presidenttipeli (presidential game) has been used it has not always been clear that the game is a game only in metaphoric sense. A game doesn't always have to be either literal or metaphoric. As a comparison, a sweet girl is, at least in English and Swedish, sweet both in a literal and a metaphorical sense. It is obvious that there is a resemblance between the sweetness of a girl and the sweetness of a berry, but both can simultaneously be literally as well as metaphorically sweet. There is a similar relationship between the computer virus and the organic virus. There are lots of examples of this kind, but they are often bound to a certain language. A notion may be based on entirely different metaphors in different languages. To change from one language to another may therefore mean changing a whole system of metaphors.
As for viruses, it is obvious that the two types mentioned belong to entirely different classes or categories. It is not certain whether the same can be said of various kinds of power. For a physicist, it may be obvious that physical energy, force and power are essentially different from other kinds of energy, force or power, but this is not necessarily obvious from a non-physical perspective. Why should a physical interaction between particles necessarily be essentially different from a social or political interaction? Whether physical power and political power belongs to completely different categories, depends on the language game the word 'power' is used in.
Members of a class do not have to be united by a single, common quality, but can instead be associated by a network of family resemblance and analogy. Ludwig Wittgenstein, who introduced the notion 'family resemblance', mentions precisely 'game' as an example of how family resemblance might keep a concept together. When in Finland the presidential election consequently has been compared to other games, people have probably more and more understood it as a literal game. This, of course, has consequences for democracy: democracy becomes a voting game, or, even worse, a game show. And not only in a pure metaphorical sense. The game is not anymore only a harmless metaphor, but it has become a dominating paradigm.
Like in politics, metaphors are common in economics. Economic phenomena are often very complex, and economic notions often lack strict definitions. What else are overheat, casino economy or economic bubble than metaphors? These metaphors make abstract and complex phenomena intelligible for laymen. Furthermore, they have a moral dimension, which directly influences financial policy. In this case it is easy to see that metaphors can be useful and even desirable. However, when politicians or journalists consciously choose and use metaphors in order to give desired "signal" or to form the opinion, the metaphors have lost their innocence.