# Teaching with Analogies

Teachers use analogies throughout their lessons, especially when responding to student questions.  When a teacher uses phrases such as “similarly”,  “likewise”, “in the same way as”, “in comparison to”, and “just like”, they are generally using analogies to help students grasp a concept.  If, however, the analogies are not well chosen or applied systematically, they may be ineffective or cause confusion.

To maximize the benefit of analogies while minimizing the dangers, we suggest that educators employ the Teaching with Analogies (TWA) strategy introduced by Glynn, Duit, & Thiele .  This strategy models what expert teachers and authors employ when using analogies.  In the TWA strategy, shared attributes between the analogue and target are known as mappings. The goal is to transfer ideas from a familiar concept (the analogue) to an unfamiliar one (the target) by mapping their relationship. The TWA model consists of the following six operations:

1. Introduce the target concept
2. Review the analogue concept
3. Identify the relevant features of target and analogue
4. Map similarities between the target and analogue
5. Indicate the limitations of the analogy
6. Draw conclusions

## Example

The following example illustrates the use of the TWA strategy when introducing the concept of a pulsar by analogizing it to the rotating lamp in a lighthouse.

1. Introduce target concept:  A pulsar is a rotating neutron start that emits radio waves in a narrow beam at regular intervals.
2. Review analogue concept:  A lighthouse contains a lamp that rotates on an axis and emits light beams to viewers at regular intervals.
3. Identify relevant features of target and analogue:  The relevant features are the source of electromagnetic radiation, the axis of rotation, the rotating source, the distant observer, and the appearance of pulsating energy.
4. Map similarities:  The neutron star at the core of the pulsar is analogous to the lamp in a lighthouse since both emit electromagnetic radiation. The spinning of the pulsar is analogous to rotation of the lamp.  The earthbound astronomer who observes pulsating energy from a pulsar is analogous to the seafarer who observes pulsating light from the lighthouse.
5. Indicate the limitations of the analogy.  The pulsar rotates at a rate of perhaps 30 times per second, while the lighthouse light rotates much slower.  The energy emitted from the pulsar is primarily in the form of radio waves, while the energy from the lighthouse is primarily in the form of visible light.  While the beam of light from a lighthouse is at right angles to the lamp’s axis of rotation, the beam of energy from the pulsar may be at various angles depending on the alignment of the magnetic pole relative to the axis of rotation.
6. Draw conclusions. The student develops a basic understanding of the pulsar by analogy to the lamp in a lighthouse.

Glynn, S. M., R. Duit, & R. B. Thiele (1995). Teaching science with analogies: A strategy for constructing knowledge. In S. M. Glynn and R. Duit (Eds.). Learning science in the schools: Research reforming practice (pp. 247-273). Mahwah, NJ: Erlbaum.