Those involved in the education of any individual child, such as a parent or teacher, can encourage the child to recognize mathematical logic that involves deductive logic constructs. For example, children will learn the mathematical principle that when c has an equal value to d, and b has an equal value to c, then d also has to equal c. You can expand this fundamental mathematical lesson to a deductive reasoning lesson by pointing out the structure of this principle and identifying it as a deductive reasoning structure.
Particularly in such literature as mystery fiction, children can find examples of deductive reasoning. Suggest that children identify the analysis of the mystery’s solution and determine whether or not it follows a deductive reasoning pattern. For example, a pattern such as: “Adrianna walked to school today, arriving promptly at 7:25 a.m. and immediately began discussing homework with her teacher, Mrs. Brooks. Mr. Compton, who runs the variety store on the corner of Adrianna’s home street, a 20-minute walk, claimed that Adrianna stole some candy and gum at the store today at 7:20 a.m. Adrianna cannot have stolen the items, however, because to arrive at school at 7:25 she would at 7:20 needed to be more than halfway to school and well past Mr. Compton’s store” illustrates deductive reasoning.
An everyday life application of deductive reasoning could include the example: “Our school is in Wakefield. Wakefield is in Massachusetts. Therefore, our school is in Massachusetts.” You can use many kinds of daily activities to illustrate deductive reasoning. For example, if you have three children of different ages and heights you can illustrate deductive reasoning through such examples as: “Mary is older than John. John is older than Kathleen. Therefore, Mary is also older than Kathleen.” You can vary this illustration by changing the final sentence from “Mary is older than Kathleen” to “Therefore, of Mary, John and Kathleen, Mary is the oldest.” You can also make this more interesting for younger children by reversing the order and starting with the youngest child and demonstrating the same style of logic, such as in the example: “If Kathleen is younger than John, and John is younger than Mary, then Kathleen is the youngest of Kathleen, John, and Mary.”
You can encourage children to practice writing such deductive reasoning classification statements as, “With root vegetables, people eat a portion of the plant that grows underground. Potatoes, carrots, turnips and beets are all root vegetables. Therefore, the edible parts of potatoes, carrots, turnips and beets all grow underground.” With animals, you can illustrate deductive reasoning with an example such as: “All horses are hooved mammals. The Lippizan, also called a Lippizaner, is a breed of horse. Therefore, the Lippizaner is a hooved mammal.” You can use this same kind of deductive reasoning lesson with breeds of other favorite animals, such as Persian or Siamese cats or collie dogs.