Botkin Environmental Science Earth as Living Planet 8th txtbk

28 CHAPTER 2 Science as a Way of Knowing: Critical Thinking about the Environment
logically from these assumptions, or premises, we say it
is proven. This process is known as deductive reasoning.
An example of deductive reasoning is the following
syllogism, or series of logically connected statements:
Premise: A straight line is the shortest distance between
two points.
Premise: The line from A to B is the shortest distance
between points A and B.
Conclusion: Therefore, the line from A to B is a straight line.
Note that the conclusion in this syllogism follows directly
from the premises.
Deductive proof does not require that the premises be
true, only that the reasoning be foolproof. Statements that
are logically valid but untrue can result from false premises,
as in the following example (Figure 2.5):
Premise: Humans are the only toolmaking organisms.
Premise: The woodpecker finch uses tools.
Conclusion: Therefore, the woodpecker finch is a human
being.
to be scientific the three statements should be expressed
conditionally (that is, with reservation):
If humans are the only toolmaking organisms
and
the woodpecker finch is a toolmaker,
then
the woodpecker finch is a human being.
When we formulate generalizations based on a number
of observations, we are engaging in inductive reasoning.
To illustrate: One of the birds that feeds at Mono
Lake is the eared grebe. The “ears” are a fan of golden
feathers that occur behind the eyes of males during the
breeding season. Let us define birds with these golden
feather fans as eared grebes (Figure 2.6). If we always observe
that the breeding male grebes have this feather fan,
we may make the inductive statement “All male eared
grebes have golden feathers during the breeding season.”
What we really mean is “All of the male eared grebes we
In this case, the concluding statement must be true
if both of the preceding statements are true. However, we
know that the conclusion is not only false but ridiculous.
If the second statement is true (which it is), then the first
cannot be true.
The rules of deductive reasoning govern only the process
of moving from premises to conclusion. Science, in
contrast, requires not only logical reasoning but also correct
premises. Returning to the example of the woodpecker finch,
FIGURE 2.5 A woodpecker finch in the Galápagos Islands
uses a twig to remove insects from a hole in a tree, demonstrating
tool use by nonhuman animals. Because science is based on
observations, its conclusions are only as true as the premises from
which they are deduced.
FIGURE 2.6 Male eared grebe in breeding season.