Preface
The aim of this book is to introduce metaphor research to the wider NLP community, and to survey the state-of-the-art in computational methods in a way that may also be helpful to those approaching metaphor from a perspective that is not principally informed by work in Artificial Intelligence (AI). We focus on the history, methods, and goals of past research into this fascinating phenomenon in the hope of making metaphor a more accessible topic of future research, thereby pushing it further up the NLP community’s wait-list. Our treatment will provide a condensed history of metaphor research that introduces the main theories of metaphor that survive, in one form or another, in contemporary analysis. Our coverage will include the main AI contributions to the field, which are modern attempts to give algorithmic form to views on metaphor that range from the ancient to the contemporary. And, just as contemporary AI research has taken on a distinctly web-colored hue, we shall explore the role of the Web in metaphor research, both as a source of data and as a computational platform for our metaphor-capable NLP systems. Computational linguistics and AI alike have each embraced statistical models as a means of improving robustness, exploiting rich veins of user data, and reducing a system’s dependence on hand-crafted knowledge and rules. Metaphor research offers no exception to this trend, and so our book will also explore the role of statistical approaches in the analysis of metaphorical language. Since such approaches are ultimately only as good as the data over which they operate, we shall also focus on the contributions of corpus linguistics to the construction of annotated metaphor corpora. Finally, we shall draw these strands together to offer an application-oriented view of metaphor, asking whether there is a killer application for metaphor research, and whether (and how) computational approaches to metaphor can help advance not only the field of NLP, but other fields as well, such as the social sciences and education. The ultimate goal of this book is not to make you believe, as we do, that metaphor is the very soul of language, though the growing field of metaphor research is always eager to welcome new converts. We will consider this book a success if readers take away a desire to address metaphor head on, in some form or another in their research, and find in this book the necessary tools to make this engagement a practical reality. Tony Veale, Ekaterina Shutova, and Beata Beigman Klebanov January 2016 CHAPTER 1
Introducing Metaphor
Language would be a dull and brittle thing without metaphor. It is metaphor and its figurative kin—simile, analogy, blending, irony, understatement, hyperbole, and the like—that lend language its vitality and elasticity. It is metaphor and its kin that allow us to suggest much more than we actually say, and to invent new ways of saying it, when conventional language shows us its limits. It is metaphor and its kin that allow us to communicate not just information, but also real feelings and complex attitudes. Metaphor does not just report the result of personal insights, but also prompts and inspires listeners to have these insights for themselves. Each metaphor is a concise but highly productive way of saying that communicates a new and productive way of seeing. But what exactly are metaphors and where do we look for them? Although metaphors are products of our faculty for creative thinking, metaphors in the wild can range from the scintillating to the banal. Just as repeated usage dulls the blade of a trusty knife, or repeated telling robs a once-funny joke of its ability to raise a laugh, repetition takes the bloom off a metaphor and turns it from an eye-catching flower into just another piece of the undergrowth. So metaphors are everywhere, in language, in film, in music, or in any system of signs that allows us to express ourselves creatively. These metaphors range from the novel to the conventional, and indeed some are so conventional as to escape our attention altogether. Nonetheless, even highly conventionalized metaphors retain a spark of the creativity that forged them, and in the right hands this spark can be fanned into a roaring fire. Consider the following example, which was used as the title of a popular science book by German rocket scientist Wernher von Braun: “I Aim For The Stars!” Since the heavens are filled with stars in any direction we care to look, von Braun could not have intended to use the word “aim” literally, which is to say “I look and/or point in the specific direction of the stars” or even (for he was a master pragmatist) “I intend to move myself physically closer to the stars.” Rather, von Braun—who was attempting to popularize the concept of space travel with the American public, and thereby win state funding for his expensive scientific work—employed a basic metaphor that allows speakers to treat PURPOSES AS DESTINATIONS. Thus, von Braun saw the achievement of interstellar space travel as his goal, and expressed this goal using the language of physical destinations. But von Braun, an ex-member of the Nazi party, was also the controversial creator of the German V-2 missiles that rained down on Britain during World War II. (He had been spirited away to the U.S. as part of operation paperclip at the end of the war, when the American and Russian militaries competed to round up the brains of the German rocket program.) The comedian Mort Sahl took full advantage of this fact, and of von Braun’s use of the PURPOSES ARE DESTINATIONS metaphor, to cheekily propose an alternative title for the scientist’s book: “I aim for the stars but I keep hitting London.” Clearly, the generic and highly reusable metaphor PURPOSES ARE DESTINATIONS is of a different character than the specific utterances that are constructed from it. Researchers refer to the former as a conceptual metaphor, for it resides at the level of thinking and ideas, and to the latter as a linguistic metaphor. Explicating the relationship between the former and the latter is one of the goals of contemporary cognitive and computational approaches to metaphor, and so we shall return to this relationship many times in this book. We’ll also meet the conceptual metaphor PURPOSES ARE DESTINATIONS again in a later chapter. We each use conventional metaphors every day, perhaps without even realizing it, yet we each have the ability to elaborate on these standard-issue constructions in our own way, to inject our own voice and personality into what we say. Consider the following quote from Twitter co-founder Biz Stone, who writes in his autobiography of how he came to be an early employee of Google: I didn’t know it at the time, but behind the scenes Evan [Williams] had to pull strings in order to hire me [at Google] (Stone [2014]). The idea of exerting influence on others by pulling [their] strings is deeply entrenched in the English language. We describe a bargain or an offer of special treatment as “no strings attached” when we believe the giver is not seeking to unduly influence us, which is to say “to pull our strings.” An emotional appeal that hits its mark is said to “tug at our heartstrings,” while we might describe a master manipulator as being able to “play someone like a violin.” A mother’s continued influence on an adult child is often given metaphoric form with the phrase “apron strings,” and any effort (by mother or child) to curtail this influence is described as “cutting the apron strings.” Stone’s use of the strings metaphor in the context of the idiom “behind the scenes” might also bring to mind images of the pulleys and ropes with which stagehands lower and raise the curtain in a theatrical production (indeed, the word “scene” gets its meaning from the piece of cloth that was draped behind the stage in ancient theatres). Metaphors are much more than the stuff of fancy wordplay, and we use them to do much more than give our messages an attractive sheen: metaphors engage fully with the mechanisms of thought, allowing us to spark associations, insights, and other metaphors in the mind of a hearer even when we are using the most conventionalized of figures. We can think of these figures as being made of clay; convention has given them their shape, but we can add fine detail of our own, or bend them further to our own meanings. Let’s look at the larger context of Stone’s metaphor: I didn’t know it at the time, but behind the scenes Evan had to pull strings in order to hire me. Actually, they were more like ropes. Or cables—the kind that hold up suspension bridges (Stone [2014]). This elaboration should dispel any doubts about whether the pulling [one’s] strings metaphor is nothing more than an arbitrary idiom that speakers
