How to know when your dog needs to go outside

Everyone who has had a dog (which is essentially everyone worth knowing) knows that dogs need to go outside for various reasons, the most obvious being the functions of the excretory system. But how do you know whether a dog really wants to go outside or is interested in something else? In this How-to I will explore this question in depth.
The most basic way a dog can tell you that it wants to go outside is through a bark. Long ago, the ancestors to modern dogs discovered that if they wanted to communicate with us humans, the easiest way was by using their vocal chords. It didn't take long for these dogs to discover that their brains were far too underdeveloped to learn human language, so they were forced to resort to barking at humans to get their attention and waiting for the more developed human brain to go to work translating the bark. The human was then expected to do whatever the dog wanted. Dogs had this down to a science, but unfortunately, this symbiosis was interrupted by the human invention of distractions. Be it a television, a book, or just pure laziness, these distractions threw off the natural order by interfering with the human's ability to translate the bark, and making the dog just seem annoying. The best thing you can do to recognize when a dog needs to go outside is to never be distracted. Instead, spend every moment following the dog and waiting for it to ask to go outside.This will prevent something as simple as "Get up off your lazy butt and open the door for me" from sounding like "I want to eat; get me some grub" or "I'm really bored; we should play fetch." The sad part is that most people are distracted all the time and are therefore unaware that dogs know how to communicate these things through bark.
The other big way to recognize a dog's need to go outside is by watching the physical signs. Sometimes dogs forget that barks are an effective form of communication, and so their desire to go outside is displayed through instinct-driven physical signs. It is important to watch these signs, but you need to be aware that the signs can be rather discreet. When a dog scratches on the door, that is quite obviously a sign that the dog wants to go outside, but there other signs that you should look for. So when you see your dog squatting on the corner of your fancy rug, don't be offended; the dog can't control its instinct. Instead of getting mad at a dog that was only doing what its body told it to, get up and open the door.