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NARRATION: What is logical reasoning? Another word for logical is sensible. We can say an idea or an answer is logical if it follows sensible rules - rules that make sense. Another world for reasoning is thinking, coming up with ideas and answers to problems. So we could say that logical reasoning is just sensible thinking. It’s about knowing the rules and working out what will happen if you follow them.

Let’s look at an example. Suppose your friend says that they want to wear a spacesuit to school tomorrow. I know, stay with me. Your friend says no one will notice. Now, you know that the school rules say that you have to wear a school uniform, or you will be sent home to change. You also know that everyone else in school will be wearing the proper uniform and your friend will look very different from everyone else in their shiny spacesuit. It’s sensible to think that they will be noticed by the teachers and sent home to change. That’s sensible thinking, based on the rules. That’s logical reasoning.

Let’s look at another real-world problem. We all love a theme park don’t we? Well, I do. This rollercoaster has a set of rules in place… The computer controlling the entry gate is programmed to open if your height is greater than 1.5m. Close if your height is less than 1.5m. Let’s predict what will happen when these people try to go through the gate using our new friend logical reasoning.

Here’s Molly, she’s 1.4m tall. Will she get through? The rule says if the height is less than 1.5m the gate will close. We know Molly’s height is less than 1.5m, so that’s easy, the gate will close, right? Let’s watch…

Lucky for me, I’m 1.7m. So, logically the entry gate will open for me as I’m taller than 1.5m and the rule says the gate will open if the height is greater than 1.5m. Here goes… OK, stop now, stop now! That wasn’t me screaming by the way… anyway!

OK, now it’s Leon’s turn. He’s exactly 1.5m tall, he’s tall enough to safely go on the ride. What do you think the gate will do? Let’s look at the rules and use logical reasoning to predict what will happen. A flow chart will help. The program rule says: If height less than 1.5m gate will close. Leon is not less than 1.5m so the gate should open… But hang on, the other rule says the gate will open only if the height is greater than 1.5m. Leon is not greater than 1.5m, so the gate won’t open… I’m confused! The system has encountered a problem. Poor Leon, how can we get him through the gate?

We need to use our logical thinking skills to change the program rules so that people who are exactly 1.5m tall can ride. So our second rule is now: If the height is greater or equal to 1.5m then open the gate. The flow chart has changed. Let’s see if that works for Leon… Yay, Leon can ride the rollercoaster thanks to our excellent logical reasoning skills.

We should use logical reasoning when we create computer programs to make them have sensible rules and instructions built-in. These rules and instructions make them good at the jobs we want them to do. A large scale example of those types of computer control systems are in the skies above our heads. No, it’s not a bird, it’s a plane.

An autopilot program on an aeroplane needs to have thousands of rules built in to calculate the speed of the plane, the effect of wind on the wings, navigating through the sky to avoid other planes and to also reach the correct destination. But the most important rule, keeping the plane 30,000ft in the air! Luckily, computers are very good at following the rules in their programs and they can do it quickly and accurately, often better than a human can.

We can also use logical reasoning to solve problems, debug, what we notice in a computer-controlled device or system. We can look carefully at the rules, decide if they are logical, and make changes if we think that will solve the problems. In short, logical thinking is awesome!