GENERATING A SPECIFIC CLASS OF METAPHORS 
Mark Alan Jones 1 
Department of Computer and Information Sciences 
University of Delaware, Newark DE 19716 
Internet: jones@udel.edu 
1 Introduction 
Although some progress has been made in the 
area of metaphor understanding, little has been 
made in metaphor generation. Current solutions 
rely upon a rather direct encoding of alternatives. 
There is no computational theory that can ac- 
count for metaphor generation from basic princi- 
ples. Although generating all types of metaphors 
from basic principles is very difficult, there is a 
subset of metaphors that are prevalent in natural 
expressions and perhaps more amenable to compu- 
tational approaches. We call these transparently- 
motivated (T-M) metaphors (Jones and McCoy 
1992). Interestingly, metaphors in general, as well 
as the class described here, can be used to achieve 
important textual goals (e.g., brevity, conceptual 
fit, focus, perspective). 
Metaphorical expressions often reflect concep- 
tual models which are the basis for how we under- 
stand the world. Mark Johnson (1987) has made 
some important observations about the building 
blocks of thought, most notably that they are tied 
closely to our bodily experience. Among the build- 
ing blocks he has described are attraction, block- 
age and containment. Consider describing the pur- 
chase of shares of stock as, "I took $2500 out of 
my money market account and put it into Exxon 
common stock." The speaker did not literally put 
money into the stock, but rather bought stock with 
the money. This metaphor is based on the simpli- 
fying concepts that represent investments as con- 
tainers which can hold money. When we write 
and talk we automatically use non-literal expres- 
sions that reflect our common conceptual ground- 
ings. These lead to very natural and easily under- 
stood expressions because we (speaker and audi- 
ence) share these common conceptual groundings. 
2 Transparently-Motivated Metaphor 
All metaphors have a mapping between two 
domains. The more literal domain is called the 
tenor domain, the less literal is the metaphorical 
domain. In the stock example these are the fi- 
nancial domain and the containment domain re- 
spectively. T-M metaphors are similar to conven- 
tional metaphors (Lakoff and Johnson 1980, Lakoff 
1987) in that they are both based upon famil- 
iar conceptual motivations. However, conventional 
metaphors are also defined in contrast to novel 
and dead metaphors. This distinction appeals to 
1This work is supported by Grant #H133E80015 from 
the National Institute on Disability and Rehabilitation Re- 
search. Support has also been provided by The Nemours 
Foundation. 
321 
knowledge about the history of expressions. In this 
sense, T-M metaphors are broader in scope, how- 
ever, in other ways they are more constrained. 
Several qualities show that the stock example 
above is transparently-motivated. It is based on 
the bodily grounding of containment. It conveys 
the verb-phrase action message of a purchase being 
conducted, which is more than merely the mapping 
from containment to purchase. This mapping is 
not even highlighted, rather it is merely used to 
convey the purchase message. 
Consider two counterexamples. The expres- 
sion, "Men are wolves" (Black 1962), is not a 
transparently-motivated metaphor. Most impor- 
tantly, its meaning is primarily the mapping itself; 
the mapping is not employed transparently to yield 
another specific meaning. 
Consider describing the starting of a business 
in terms of gardening. "You must plant the seed 
in fertile soil, give it plenty of water..." Such al- 
legorical metaphors are not T-M because they do 
not have a referent from the tenor domain which 
remains unchanged by the metaphor (e.g., "shares 
of stock"). The scope of this work is further con- 
strained to metaphors that convey a verb=phrase 
meaning. The bounds of T-M metaphors that pri- 
marily convey other meanings, such as reference, 
are less clear. 
So, transparently-motivated metaphors: 1) 
Are based on universal groundings that are of- 
ten linked to bodily experience; 2) Convey a mes- 
sage (via the mapping) that is something more 
than the mapping; 3) Are subtle in the way that 
they do not draw attention to themselves as bla- 
tant metaphors. In fact, at first glance, these 
metaphors are often not recognized as non-literal; 
4) Retain a referent from the tenor domain. 
3 Uses of Metaphor 
Metaphor is not merely a device that adds a 
flowery flavor to text. Rather, metaphor can be 
harnessed to achieve textual goals that may be dif- 
ficult to achieve with literal statements. A simple 
goal that metaphor can achieve is that of being 
concise. More complex uses are explained below. 
3.1 Conceptual Fit 
We noted that the building blocks of thought 
may lead us to speak metaphorically. It is rea- 
sonable to conclude that metaphors based on such 
building blocks are easier to understand because 
they reflect human conceptualizations. 
Two observations are salient. People naturally 
tend to describe things in a more concrete manner, 
even when the issue at hand is rather abstract. 
Such behavior generally yields more natural and 
understandable text. This explains why expres- 
sions like, "grasping an idea" are common. Second, 
it is natural to talk about things in the light of ba- 
sic building blocks of thought that are commonly 
shared by a community. Therefore, describing a 
stock transaction as putting a token in a container 
may be more intuitive to the audience. 
3.2 Focus of Attention 
The traditional view of focus of attention is 
that it is something that is accomplished syntacti- 
cally, such as by making the desired focus the sub- 
ject of the sentence (as can be done with a passive 
construction). However, further inspection reveals 
that there is a relationship between semantic types 
and level of focus. 
Jones and McCoy (1992) show evidence for 
the intuitive proposition that the semantic types 
of words/concepts affect the perceived level of fo- 
cus attributed to those words/concepts. We intro- 
duce a simple focus hierarchy to model the effects 
of semantic types on focus levels. Items at the top 
of the focus hierarchy, because of their semantic 
qualities, are more likely to be focused upon than 
those below. Generally, concepts which are very 
concrete and volitional are toward the top while 
more amorphous and abstract things are below. 
Given the focus hierarchy which explains in- 
herent focus level according to the semantic type 
of an object, it is interesting to note that one 
effect of metaphorical statements can be to al- 
ter the perceived semantic type of an object 
(and therefore potentially raise the perceived focus 
level). Consider the metaphorical statement "AI is 
no stranger to object-oriented paradigms" (Elliot 
1991). Notice that the phrase "is no stranger" has 
the effect of conceptually personifying the objects 
involved (i.e., AI and object-oriented paradigms) 
since it is a phrase that, literally, can only be 
used with humans (or perhaps other animate ob- 
jects). Compare the perceived focus level with that 
in a more literal rendition of the sentence such 
as: "AI and object-oriented paradigms have previ- 
ously been incorporated together." 
In the traditional view of focus of attention a 
word is treated as having a static semantics. How- 
ever metaphor can make the semantic type of ob- 
jects more flexible. By using a verb that only ap- 
plies to humans, as above, the objects are pushed 
up the focus hierarchy towards the position that 
humans occupy. 
3.3 Perspective 
While the notion of perspective on an item is 
related to focus, they are distinct. Rather than 
concentrating on which object is focused on, per- 
spective has to do with how an object is viewed. 
A given perspective on an item causes certain as- 
pects of that item to be highlighted (and not oth- 
ers) (McCoy 1989). 
322 
Consider a couple with young children attend- 
ing a party with all of their children's parapher- 
nalia in tow. One tells the other "It is time 
for us to pull up stakes." Here, the leaving is 
metaphorically described via the camping domain, 
where leaving is an involved process. This use of 
metaphor has highlighted or put a particular per- 
spective on the leaving that emphasizes the work 
involved. 
4 Approach to a Solution 
T-M metaphors are a promising sub-class of 
metaphors in which to work, because they carry 
special requirements that restrict the possible 
search space from which they can be generated. 
We have begun preliminary work to specify the 
basic structures and methodologies that together 
can generate good metaphors. Input to the sys- 
tem has two parts. The first part is the literal 
statement of what should be expressed, in a for- 
mal form. For example, describe the leave role of 
the object party. The second part of the input to 
the system is a specification of the goal that the 
metaphor is to achieve. 
4.1 General Approach 
The idea behind the approach is to identify re- 
lated domains of the tenor domain that are appro- 
priate as metaphorical domains. Both the tenor 
and metaphorical domains share some roles that 
are defined by their common ancestor in the "is- 
a" hierarchy. Specifically, we require that they 
share the role that is the focus of the metaphor 
(that aspect of an action which is being referred 
to metaphorically). We can identify an ancestor 
of the tenor domain from which the tenor domain 
inherits the role in question. The metaphorical do- 
main also will share this ancestor. 
In addition to sharing the common ancestor, 
a reasonable metaphorical domain must have the 
following qualities: 
• Be universal, or considered very familiar 
(with respect to the user model}. If the audi- 
ence is ignorant of the metaphorical domain, 
there is little hope of the expression's success. 
• Have the potential to achieve additional goals 
(e.g., focus). 
• Have specialized iexical expressions in the 
metaphorical domain for the role being de- 
scribed. This is necessary because the lexi- 
cal expression used to describe the role is the 
only information that conveys the mapping. 
This restriction would not apply to non-literal 
expressions that explicitly state the mapping. 
Without the specialized lexical expression, a 
T-M metaphor cannot be generated. 
These specifications constrain what potential 
metaphorical domains will be considered. By lim- 
iting the candidate domains, the space and search 
time requirements will be held down. 
Consider how we can generate the metaphor- 
ical expression conveying "leave the party," while 
at the same time emphasizing the effort that it 
takes to leave (as in section 3.3). A party can be 
described, via "is-a" links of the abstraction hi- 
erarchy, as a human process. Such a process can 
have a termination. For partying, leaving and say- 
ing goodbye to everyone can be considered part of 
the termination of this process. 
After ascending the "is-a" hierarchy to the 
proper level of abstraction, where the key role (ter- 
mination) is specified, we can search for a can- 
didate metaphorical domain that shares this an- 
cestor. There are several possible metaphorical 
domains that meet this criteria. To narrow this 
choice several considerations come into play. 
One of these considerations is whether the pos- 
sible metaphorical domains have specialized ex- 
pressions available for the role that the metaphor 
involves (termination). Two possible metaphorical 
domains that meet this criteria are camping, with 
"pulling up stakes," and electrical equipment, with 
"pull the plug." 
Both domains are potential candidates. How- 
ever, now the constraints imposed by the goal of 
the metaphor must be considered: emphasize the 
complexity of the termination. Will an allusion to 
camping rhetorically make leaving the party ap- 
pear more involved? Here we must appeal to more 
detailed knowledge about the termination of the 
camping experience. In this case we find that the 
termination of a camping experience is not trivial, 
it requires a moderate amount of work (compared 
to the party and electrical domains). Therefore the 
camping domain may be chosen. Other metaphor- 
ical goals (e.g., focus) will cause different reasoning 
to be done in this final stage. 
4.2 Specific Conceptual Mappings 
The previous approach may work well for some 
T-M metaphors, but notice there is a severe re- 
striction on the relationship between the tenor and 
metaphorical domains - they must have the role 
involved in the expression in common. Here we 
discuss how the previous method can benefit from 
additional information, which can link two very 
different domains. 
Recall from section 3.1 that conceptual fit 
is a motivation for metaphor generation. The 
method introduced here helps implement the prin- 
ciple that it is useful to describe things in terms of 
shared conceptual roots. If a system is to generate 
metaphors that follow from conceptual roots, those 
roots must be represented in the system. We will 
need metaphorical domain selection rules and re- 
lated mapping information to capture the concep- 
tual roots by reflecting such common metaphorical 
behaviors as those pointed to in Lakoff and John- 
son's work (Lakoffand Johnson 1980, Lakoff 1987). 
Selection rules will encode such familiar patterns 
as "describe progress in terms of a vehicle moving 
toward a goal" and "describe securities in terms of 
containers for money." 
Consider describing the progress with a pub- 
lication or career, with the intention of being as 
323 
Table 1: Progress in terms of a moving vehicle 
Tenor Domain Met. Domain 
progress ....... forward 
negative progress ....... backward 
no progress ....... still 
unsatisfactory progress ....... slow 
intuitive as possible (conceptual fit). A rule en- 
coding the notion "describe progress in terms of a 
vehicle moving toward a goal" would be triggered. 
Closely attached to this rule is information about 
how the mapping from tenor domain to metaphor- 
ical domain should relate. Such information would 
include the mappings in Table 1. 
Notice that these expressions for progress in 
the domain of physical motion are natural and 
probably-more frequent than the "literal" forms 
found on the left side of Table 1. This may be be- 
cause people understand progress in terms of mo- 
tion. In this way metaphor generation can yield a 
more conceptually appropriate expression, which 
may actually be easier to understand than its lit- 
eral counterpart. 
There is potential for abstracting the informa- 
tion in the table. Note that the moving object has 
some starting point, some goal and some points on 
its path. With time involved, it also has speed. 
With a sophisticated model of this behavior in the 
metaphorical domain available, the four mappings 
in Table 1 could be derived. Interestingly, a more 
general structure matched with reasoning in the 
metaphorical domains could derive other expres- 
sions. With the knowledge that energy is required 
to move objects, and given that a prototypical 
moving object is a car that runs on gas, we could 
hope to generate "My career is running out of gas" 
from general knowledge and principles. 

REFERENCES 
Max Black (1962). Models and Metaphors. Cornell 
University Press, Ithica, NY. 
Lance B. Elliot (1991). The bandwagon blues. AI 
Expert, 6(5):11-13. 
Mark Johnson (1987). The Body in the Mind: The 
Bodily Basis of Reason and Imagination. Uni- 
versity of Chicago press, Chicago, IL. 
Mark A. Jones and Kathleen F. McCoy (1992). 
Transparently-Motivated Metaphor Generation. 
In R. Dale, E. Hovy, D. Rosner and O. Stock, 
eds., Aspects of Automated Natural Language 
Generation: The 6th International Workshop 
on Natural Language Generation Proceedings, 
Trento, Italy. 231-246. 
George Lakoff (1987). Women, Fire and Danger- 
ous Things What Categories Reveal About the 
Mind. University of Chicago Press, Chicago, IL. 
George Lakoff and Mark Johnson (1980). 
Metaphors we live by. University of Chicago 
Press, Chicago, IL. 
Kathleen F. McCoy (1989). Generating context 
sensitive responses to object-related misconcep- 
tions. Artificial Intelligence, 41:157-195. 
