Some time ago we bought the Penguin Collection of Sherlock Holmes. This is a series of eight books that bring together the novels and short stories by Sir Arthur Conan Doyle. I started looking through them to try to find where Sherlock Holmes uttered those famous words: “Elementary my dear Watson!”
The great detective used the words, to Watson’s utter frustration, when he was demonstrating reasoning to solve a perplexing case.
He drew logical conclusions from certain premises – and these are known as `deductions’.
He made brilliant generalisations on the basis of specific details – and these are called `inductions’.
Children working towards the eleven plus will sometimes make deductions and at other times inductions. Sometimes parents may find it difficult to see which route their child is following.
In the analysis of an answer a parent with a supremely tuned logical mind may prefer to answer some types of questions by following careful and predictable steps. Their eleven plus child, however, may prefer to read the question remarkably quickly and throw out an inspired induction.
Take the hoary old question.
Three policemen, two on foot and one with a motorbike, picked up three robbers. The policemen feared that the robbers would flee as soon as they (the policemen) were outnumbered.
The motor bike would only carry two.
The policemen could not be put into a position where they were outnumbered.
In what order should the robbers be transported?
Traditionally the answer is that the two robbers ride off to the police station – then one robber rides back. This won’t always work – as the robbers may take off at high speed.
One kind of brain will continue to try to analyse the question – even though it is simple nonsense. A different kind of brain would suggest the policemen call immediately for backup. At this stage, however, it is difficult to work out which conclusion was reached by deduction and which by induction. Please help!