**Testing hypotheses (cont.)**

*test
implications*—are
normally conditional (if-then) statements of the form,

“If conditions *C* occur then
event *E* will occur”

“conditions
*C*”:

·
Conditions
of some experiment

·
Observed
conditions

“If *H* (test
hypothesis) and *A* (auxiliary hypothesis) are true, then *I* (test
implication) is

true.”

*Example*—

If *childbed fever is
caused by infectious matter* (*H*) and *chlorinated lime*

*destroys infectious matter *(*A*), then if*
persons attending the patients wash*

* their hands in a chlorinated lime* *solution *(*C*)*
deaths from childbed fever will*

* be reduced* (*E*)*.*

*Forms
of reasoning involving auxiliary hypotheses*—

Case 1—the test implication is true:

If *H* and *A* are
true, then *I* (if *C* then *E*) is true.

*I* is true.
(observation or outcome of experiment)

Therefore, *H* is true.

Case 2—the test implication is false:

If
*H* and *A* are true, then *I* (if *C* then *E*) is
true.

*I* is false.
(observation or outcome of experiment)

Therefore, either *H* or
*A* (and possibly both) are false.

According
to Hempel, in order for a statement to qualify as a *scientific hypothesis*,
it must be

__empirically testable in
principle__

[I.e., There must be some *conceivable*
observation or experiment the results of which

would
determine the truth or falsity of the hypothesis’s test implication.]

__ __

*pseudo-hypothesis*—a statement that appears to
be a scientific hypothesis but fails the

condition of empirical testability in principle

*crucial
test*—a test
(experimental or observational) intended to determine which of two

rival hypotheses is true
and which is false

reasoning—

If *H _{1}* is
true, then

If *H _{2}* is
true, then

[*E _{1}*
and

*C* and *E _{1}*.
[outcome of experiment]

Therefore, *H _{1}*
is true and

Example—

the “tower experiment” to
decide between the geocentric (earth-centered) and

heliocentric (sun-centered)
theories of the solar system

1.
Because
*auxiliary hypotheses* are almost always needed to derive test
implications from test hypotheses, it is impossible to *disprove* either
of two competing hypotheses.

2.
Test
hypotheses cannot be “conclusively proved by any set of available data.” (pp.
27-28)

*ad
hoc *hypothesis—an
auxiliary hypothesis introduced for the sole purpose of saving a test

hypothesis
being threatened by adverse evidence

*example*—the phlogiston theory: phlogiston as having negative
weight

1.
There
is no precise criterion for *ad hoc* hypotheses.

2.
An
a*d hoc *hypothesis is motivated by the desire to protect someone’s
favored test hypothesis from refutation by the results of experiments.

3.
Generally
speaking, an *ad hoc* hypothesis leads to no additional test implications.*
*