 When we talk about grammar, we're really talking about the structure beneath our language. And understanding that structure is the key to getting little mechanical details like comma's right. The first step is identifying the two pillars upon which the whole structure rests. The subject and predicate are less things than they are roles, and we define them by their relationship to each other. Kind of like we define brother or sister by relationship. It makes them incredibly versatile, especially the subject. That's great for our speaking and writing and thinking, but it can make the subject hard to pen down with any single definition. We're going to try it, but first let me offer a simpler definition. The subject is usually, one, the noun that serves as the topic of the sentence, two, at the beginning of the sentence, and three, the doer of the action in the sentence. Let's look at a simple example. The robot dances. What's the noun that serves as the topic, the beginning of the sentence, and the doer of the action? The robot. That's the subject. And it remains the subject, even if we add a lot of other information. The robot dances through a crosswalk in front of a Walgreens. The robot is still the topic, the beginning, and the doer. In more complicated sentences, we sometimes have to settle for two of three. An introductory phrase can push the subject away from the beginning. After being painted in rainbow stripes, the robot keeps dancing. Because the robot is still the topic and the doer, we know it's still the subject. A sentence can also be flipped into passive voice, which takes the doer of the action out of the subject slot. The robot is being upstaged by two visored humans. The humans are doing the upstaging, but the robot is still the topic and the beginning so we know it's the subject. But sometimes, something other than a noun gets shoved into the subject slot, like a verb phrase, to dance with a robot is divine. The subject is to dance. Other times, a whole clause can serve as a subject. All the boy wants is to dance the robot in front of Buckingham Palace. The subject is all the boy wants, and that clause has its own subject, the boy. As you can see, it can get pretty complicated, and that's why these simple definitions ultimately come up short. It's also why the best way to recognize a subject is to consider its relationship with the predicate. Trying to do otherwise is like trying to define brother or sister without mentioning a sibling. Because the link between them is the foundation of our sentences, a more functional definition for a subject might be the element that controls the predicating verb. Whether the subject is a noun or not, that verb should always remain in lockstep with it, like a dancer following its partner's lead. When we say the robot dances, for example, we choose the form of that predicating verb, dances, based on the subject. The robot dances, but the robots dance. The subject controls the form of that verb, and that's true of all the examples we've looked at. The robot is upstaged by humans, but the robots are upstaging the humans. To dance is divine, but to dancing robots are divine. Now in English, unlike some other languages, we have a lot of conjugations that remain the same across different perspectives. I danced, you danced, she danced, they danced. Even so, the subject, I, you, she, they, has control of the verb in a way that you can probably sense with your natural intuition as an everyday language user. That control will remain no matter what form the subject takes, where it occurs, or how many there are in a sentence.