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# ●    What are two main characteristics that make something reliable as explained through the thermometer

example?

What Makes a Thermometer Reliable?
The Reliability Theory of Knowledge claims that there is an important analogy between
knowledge and a reliable measuring device. If you know that there is a page in front of you
now, then your belief is related to the world outside your mind in the same way that the
reading of a reliable thermometer is related to the temperature.
Thermometers are devices that form representations of temperature. The height of
the mercury column is the representation; the ambient temperature is the thing repre-
world outside your mind. Thermometer readings can be accurate or inaccurate, just as
beliefs can be true or false. What makes a thermometer reliable? Does this just mean that
Chapter 14: The Reliability Theory of Knowledge
163
its readings are accurate? To see why this isn't enough, consider a thermometer that is used
just once. Suppose, on that one occasion, the thermometer said &quot;98&quot;F&quot; and the temperature
happened to be 98&quot;E. The reading was accurate, but that doesn't mean that the thermom-
eter was reliable. For all I've said, the thermometer may be broken-perhaps it would say
&quot;98&quot;F&quot; no matter what the true temperature is. If so, it isn't reliable, even though its one
and only reading was accurate. A reliable thermometer is one for which there is a connec-
tion between readings and temperatures. If the thermometer reads n degrees Fahrenheit,
then the temperature must be n degrees Fahrenheit. If a thermometer is reliable, then its
reading must be correct; it can't be mistaken in what it says. A stuck thermometer isn't rell-
able, even when its readings happen to be correct. It is unreliable because its readings are
correct only by accident.
Do reliable thermometers exist? I think so. The mercury thermometers we use to
check whether we have fevers are examples. In saying this, I'm not denying two obvious
facts. First, a thermometer can be reliable in one set of circumstances but not in another.
A mercury thermometer wouldn't be very useful for measuring temperature if it were
wrapped in insulation before being placed in your mouth. The second point is that in
saying that a thermometer Is reliable, I'm not denying that it would be unreliable if it were
broken. Hitting a reliable thermometer with a hammer will usually be enough to make it
unreliable. So there are two things that help make a thermometer rellable. First, it has to be
used in the right environment (for example, don't wrap it in Insulation if you want to take
somebody's temperature). Second, the internal makeup of the device has to be right (for
example, the glass tube that holds the mercury can't be broken).
. Notice that reliability is an objective feature of the relationship between the thermom-
eter and its environment. The question is whether the thermometer and its environment
make the following claim true: If the thermometer says that the temperature is n degrees
Fahrenheit, then the temperature must be n degrees Fahrenheit. It is an entirely separate
question whether anybody realizes that this thermometer/environment relationship
obtains, Whether we notice this fact is a subjective question, but whether the relationship
obtains is an objective matter.
Let's imagine that you take a thermometer out of a child's mouth, see that it reads 99&quot;E,
and then announce: &quot;The thermometer is reliable, and so the baby's temperature is 99&quot;E&quot;
Suppose a contentious philosopher (like me) comes along and tries to refute your claim.
I say:
Your thermometer isn't reliable. It is unreliable because I can conceive of a circum-
stance in which its reading would be false. For example, I can conceive of a situation
in which the thermometer is wrapped in insulation. In that case, the thermometer
reading wouldn't be correct. I also can conceive of the thermometer's being broken.
In that case as well, the thermometer reading wouldn't be correct. It follows from the
fact that I can conceive of these things that your thermometer isn't reliable.
Should you be convinced by my argument? I think not. Whether the thermometer is rell-
able here and now has nothing to do with what I can imagine. Granted, if the situations
I described actually obtained, then the thermometer wouldn't be reliable. But from this it
doesn't follow that the thermometer is unreliable in the actual circumstances in which it
is used.

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