What is sentiment analysis?

Many texts contain language that can be described as emotional. Whether to express the feelings of the writer, or to inspire a particular feeling in the reader, human language can convey anger, disappointment, disgust, joy, happiness, amusement, and so on. Discovering this type of emotional content can tell us a great deal about the writer, including what the writer's intention was and the expected response of the reader. Even noticing the absence of emotional content in a text can be interesting. Once we understand how to discern the emotional content of a text, or lack thereof, we can compare texts and writers to each other in terms of the emotional content, we can compare emotional content over time, and we can sometimes even predict how a reader will respond to a particular text.

Analyzing a text for its emotional content can take many forms. In this chapter, we will be primarily concerned with sentiment analysis, sometimes called opinion mining. Sentiment...