Ch. 4— Ethical Considerations • 75 
curred with Descartes that the human mind was 
capable of creatively entertaining a variety of pos- 
sible conclusions from a given body of experience. 
But this, Hume argued (29), was nothing more than 
a habit of inference formed from repeated obser- 
vations, something that dogs could do as well (30): 
Tis necessary in the first place, that there be 
some impression immediately present to their 
memory or senses, in order to be the foundation 
of their judgment. From the tone of voice the dog 
infers his master’s anger, and foresees his own 
punishment. From a certain sensation affecting 
his smell, he judges his game not to be far distant 
from him. 
Secondly, the inference he draws from the pres- 
ent impression is built on experience, and on his 
observation of the conjunction of objects in past 
instances. As you vary the experience, he varies 
his reasoning. Make a beating follow upon one 
sign or motion for some time, and afterwards 
upon another; and he will successively draw 
different conclusions according to this most re- 
cent experience. 
The issue dividing Descartes and Hume survives, 
still unsettled, in current controversies over artifi- 
cial intelligence and animal cognition. Recent decades 
have witnessed an explosion of empirical inves- 
tigations into the behavior of nonhuman animals 
(26,35,50). Among these, various efforts to teach 
higher primates how to use a nonverbal language 
have captured the public's imagination. Inferences 
drawn from such studies, however, encounter two 
obstacles. First, to argue that chimps consciously 
use gestures in the same way that human deaf- 
mutes do is to assume a certain theory about the 
relation between bodily behavior and mental oper- 
ations. No consensus on mind-body relations exists 
today. The same difficulty, it is worth noting, af- 
fects various efforts to use similarities in brain 
structure and function as evidence for similari- 
ties in thought. 
Even if such matters could be resolved, a greater 
conceptual hurdle would remain: What is the con- 
nection between language and thought? Language 
requires combining terms into well-formed sen- 
tences using rules of grammar and meaning. Lin- 
guistic mastery includes the capacity to create 
novel sentences in situations not precisely like 
those already encountered and the resources to 
express thoughts in different modalities (as descrip- 
tions, questions, commands, and so on) (48). It also 
seems to require recognition that something said 
is true, false, or uncertain (17,24). 
Although no one knows whether other primates 
will ever approach human beings in linguistic per- 
formance, it would be a mistake to focus on that 
issue. Evidence is mounting that animals can rec- 
ognize visual patterns, remember where their food 
is located, learn how to perform nonmechanical 
tasks , and foresee where a moving prey will even- 
tually be positioned, even if they cannot master 
a language (26,50). In this sense, animals exhibit 
intelligence as defined by ability to adapt to envi- 
ronmental conditions. From a Darwinian (evolu- 
tionary) perspective, humans do not hold a privi- 
leged status over animals. Humans are not more 
highly evolved than other animals; all have evolved 
to fill their respective niches. 
Neither linguistic nor nonlinguistic findings hold 
all the answers. The moral issue is not simply 
whether animals have some and lack other abili- 
ties that human beings possess, but whether the 
differences between them make for differences 
in how humans and animals should be treated. 
Sometimes the differences matter, common sense 
might say, and sometimes they do not. 
THE ETHICAL QUESTIONS 
How, if at all, should animals be used in research, 
testing, and education? Before this can be answered, 
a preliminary question must be asked (14,15,44,47): 
What moral standing does an animal have? Is it 
the kind of being to which humans could possibly 
have moral duties and obligations? Taking one side 
or another on the question need not include any 
particular moral judgment. Whatever its resolu- 
tion, the separable moral issue remains: What con- 
straints, if any, regulate humans' use of animals? 
These constraints might be weaker if animals lack 
moral standing, but not necessarily absent al- 
together. 
