 The universe is a big place. Huge in fact, and rather complicated. Unfortunately the human brain is relatively tiny and simple, at least in comparison. To help you survive it has to work hard to make sense of things. It does have some clever tools to help it achieve this. It can turn experiences into symbols, recall sensations and identify patterns. But most mental tricks take a lot of energy and so your brain takes shortcuts. For example it will seek out ideas that confirm what you already suspect. It will find the ideas of people you trust to be more appealing than those of people you don't. It will take your own experience and treat it as evidence. It will blur the lines between what you feel to be the case and what you know to be the case. Most of the time these tricks serve us so well we're hardly even aware of them. But sometimes they mislead us. The biases which can be so useful can also blind us. And in a complex world of differing opinions it's hard to know when to think using shortcuts when to put some effort into using our heads. Thinking doesn't always need to be hard however. Logic is a useful way to identify ideas that are likely to be helpful. Logic is a way to combine ideas to come to a conclusion. It's like maths, only it can deal with more than numbers. You've probably used it already. Think about the last argument you had. Did it go a little something like this? But everyone else is allowed to go, why can't I? A logical argument would be structured, all people are allowed to go, I am people, therefore I should be allowed to go. Logic is a useful way to combine established ideas to support the acceptance of a new idea. Looking for logic in an argument can help you decide whether you should agree with somebody or wait for more information.