TOK Induction Deduction Activity
Scientific magic experiments to illustrate deductive and inductive reasoning
Who can resist a little magic trick? You don't have to be a magician to perform these tricks.
You will turn water into wine, and then cola.
The tricks illustrate that we all use inductive reasoning to make sense of the world. When we see something unexpected we can't believe our eyes. Inductive reasoning is no further help. With a little chemical knowledge, and a few clues we can deduce what has happened, like a true detective, or more precisely like a real scientist. This is a type of deductive reasoning.
Aim: To learn that within the Scientific method there are two types of reasoning.
Activity 1: Pouring a colourless liquid to illustrate inductive reasoning
Everyone has poured many glasses of water, and so we have already made plenty of observations of pouring liquids and thus we have reached some general conclusions using inductive reasoning.
- Measure 50ml of tap water and pour it through a range of glassware and return it to the measuring cylinder.
- Make a list of the things you know about pouring colourless liquids.
- Answer the questions on the worksheet.
Activity 2: Magic - turing water into wine
- Collect a 'Magic' beaker from your teacher.
- Pour your 50ml of colourless liquid into the magic beaker.
- What happened?
- How would we use the Scientific method to explain this 'magic'?
- Answer the questions on the worksheet.
Demonstration: Further Magic - from wine (or blackcurrent juice) to Cola and 'Champagne'
- The teacher may organise a demonstration (see the link to lab preparations) or you can watch this video to see a few other chemical magic tricks.
- Answer the the questions on the extension work page (if you have time)
Description: Teachers notes about how to use the activity.
Activity 1: Pouring water into lots of different glassware.
Students can do this safely. There are many examples of scientific generalisations which will come out of this simple activity. Liquids change shape, they take the shape of their container, they have surface tension, they stick to the sides of the glassware, etc.
We use inductive reasoning to reach these general conclusions. It is good to point this out to students.
Ask students what they know about pouring water - Draw out the facts that; shape changes, volume stays the same, ask about colour, mass, surface tension, hydrogen bonding - do they change in different containers.
Activity 2: Student using 'magic beakers' to change water into blackcurrent juice,
Students follow the simple instruction to observe carefully as they pour the liquid into the magic beaker.
Inductive reasoning tells us that the liquid should remain colourless.
When it turns violet we can no longer use induction, unless we have seen coulourless liquids turn violet when we pour them lots of times before.Ask students to think of hypotheses about what happened.
They will make many suggestions of the causes, indicators, acids etc, and will have started a process of deductive reasoning.
We can deduce what has happened, using deductive reasoning and the Scientific method. This has been described as guessing what could have happened, making testable predictions and carrying out a further test to see if our guess is correct.
Demonstration of other chemical supprises - mostly for fun.
Water, Wine, then cola, and perhaps champagne - see protocol.
Plenary / General Points
- inductive reasoning comes from lots of observations of something, leading to a generalisation which is true in neally all cases.
- deductive reasoning is a process of logical steps which lead to a specific conclusion.
- Scientific method is the creation of many hypotheses which are tested by experiment, and deductive logic.
- One experiment can support a hypothesis, but this doesn't make it certain
- One experiment can disprove a hypothesis with certainty.
- Deduction could also be described in Science as, the step by step disproval of lots of different hypotheses until the only one is left 'not disproved'. This is therefore the best Scientific explanation.
David Faure, 2012.