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Theory of Inventive Problem Solving (TRIZ) 287

or at least they are not harmful, but they do not provide benefits
directly to the customer and they incur costs. Harmful functions are
not useful and provide no benefits at all.

Functional statement. A function can be fully described by three ele-
ments: a subject, a verb, and an object. For example, for the automo-
bile, its main basic function can be described as:
Car moves people
(Subject) (Verb) (Object)
For a toothbrush, its main basic function can be described as

Toothbrush brushes teeth
(Subject) (Verb) (Object)

Functional analysis diagram. A functional analysis diagram is a graphi-
cal tool to describe and analyze functions. The following graph is a typ-
ical template for functional analysis diagram:

Action
Subject Object
or Field
where the subject is the source of action, the object is the action receiver.
Action is the “verb” in a functional statement, and it is represented by
an arrow. In a technical system, the action is often being accomplished
by applying some kind of field, such as a mechanical, electrical, or
chemical field. For example, the function “brush teeth” can be
described by the following functional analysis diagram:

Brush
Toothbrush Teeth
Mech.
In the above diagram, “Mech” stands for “mechanical field.” Clearly,
brushing teeth is an application of one kind of mechanical field,
force. In a functional analysis diagram, there are four types of
actions, and they are represented by four types of arrows as illus-
trated in Fig. 9.1.

Example 9.1. Brushing Teeth If we use a toothbrush correctly, and our teeth
get cleaned properly, then we call this brushing action a “normal useful
action.” We can illustrate that by the following functional analysis diagram:

Brush
Toothbrush Teeth
Mech.