Dangers of (starting with) definitions

Definitions in scienceIt makes perfect sense. We want our students to learn about the concept of osmosis and so we start with a definition.

Teacher: “Good morning class, today we are going to learn about osmosis. Please copy down the definition from the board as this will help you to understand. Osmosis is the net movement of water molecules from an area of high water concentration to an area of low water concentration through a selectively permeable membrane.”  Johnny, what’s osmosis?

Johnny: “Osmosis is the net movement of water molecules from an area of high water concentration to an area of low water concentration through a selectively permeable membrane.”

Teacher: “Excellent! Well done Johnny.”

And stop.

Why are definitions dangerous?

Definitions are dangerous and let me try and explain why. From the perspective of the expert i.e. the teacher they are useful. They are useful because they make sense. The teacher understands the concepts of molecules, net movement, concentration and membranes. But this is not the case for the students. For them the definition is an incredibly abstract starting point- they are defining words that for the most part, cannot be seen and do not relate to their pre-existing knowledge.

Let’s try some other examples and see if they help you?

A plesiomorphy refers to the ancestral trait state, usually in reference to a derived trait state. A symplesiomorphic trait is also shared with other taxa that have an earlier last common ancestor with the taxa under consideration

Crore (noun) indian ten million; one hundred lakhs, especially of rupees, units of measurement, or people.

Were these definitions helpful in understanding? Well, I suppose only if the context and words used in the meanings are familiar and understood. If you studied evolutionary biology or travelled to India then the definitions are useful. It sounds an obvious point, but I think we all need reminding that glossaries and definitions are useful, but only if students can understand the context and terms used. This is unlikely to be the case when definitions are used as the starting point in lessons.

Helping students understand new words

  • Show pictures of key terms
  • Act out key terms – I used to smash the metal filing cabinet to demonstrate sonorous
  • Ask students to draw what the words mean e.g. a drawing to represent selectively permeable will give you a huge amount of feedback as to whether they understand this term
  • Ask students to identify errors in definitions
  • Ask students to replace certain words with synonyms
  • The Science Penguin has produced a fantastic resource to teach key words through small group hands-on examples of the vocabulary terms.

So, definitions can be useful. But they are most useful for experts who have forgotten and are least useful for novices who are learning. And yes, there is a time for students to learn definitions in science – but they must understand the terms they are defining.

  1. Dangers of starting with definitions 
  2. Developing oracy for science 
  3. Reading for meaning in science