Understanding Psychology (10th Ed)

functional fi xedness
The tendency to 
think of an object only in terms of its 
typical use.
mental set
The tendency for old 
patterns of problem solving to persist.
FIGURE 8 
The problem here is to place 
three candles at eye level on a nearby 
door so that the wax will not drip on 
the fl oor as the candles burn—using 
only material in the fi gure. For a solution 
turn to Figure 10 on p. 260.
FIGURE 9 
Try this classic demonstration, 
which illustrates the importance of 
mental set in problem solving. The 
object is to use the jars in each row to 
measure out the designated amount of 
liquid. After you fi gure out the solution 
for the fi rst fi ve rows, you’ll probably 
have trouble with the sixth row—even 
though the solution is actually easier. 
In fact, if you had tried to solve the 
problem in the sixth row fi rst, you 
probably would have had no diffi
culty 
at all.
A 
B 
C 
1. 
2. 
3. 
4. 
5. 
6. 
100 
21 
99 
5 
21 
31 
25 
14 
18 
9 
20 
28 
127 
163 
43 
42 
59 
76 
3 
25 
10 
6 
4 
3 
Given jars with these capacities (in ounces): 
Obtain:
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260 Chapter 
8 
Cognition and Language
Mental set can affect perceptions as well as patterns of problem solving. It can 
prevent you from seeing beyond the apparent constraints of a problem. For example, 
try to draw four straight lines so that they pass through all nine dots in the grid 
below—without lifting your pencil from the page.