Inference is a mental process by which we reach a conclusion based on specific evidence. Inferences are the stock and trade of detectives examining clues, of doctors diagnosing diseases, and of car mechanics repairing engine problems. We infer motives, purpose, and intentions.

Inference is essential to, and part of, being human. We engage in inference every day. We interpret actions to be examples of behavior characteristics, intents, or expressions of particular feelings. We infer it is raining when we see someone with an open umbrella. We infer people are thirsty if they ask for a glass of water. We infer that evidence in a text is authoritative when it is attributed to a scholar in the field.

We want to find significance. We listen to remarks, and want to make sense of them. What might the speaker mean? Why is he or she saying that? We go beyond specific remarks to underlying significance or broader meaning. When we read that someone cheated on his or her income taxes, we might take that as an example of financial ingenuity, daring, or stupidity. We seek purposes and reasons.

Inferences are not random. While they may come about mysteriously with a sudden jump of recognition, a sense of "Ah ha!," inferences are very orderly. Inferences may be guesses, but they are educated guesses based on supporting evidence.The evidence seems to require that we reach a specific conclusion.

Evidence is said toimply; readersinfer. While this image suggests an intent or power on the part of evidence that does not exist—how, after all, can a fact compel a certain conclusion?—the image and resulting terminology are useful nonetheless. The sense of inevitability to the conclusion suggests that we did not jump to that conclusion or make it up on our own, but found it by reasoning from the evidence.

The above image implies that everyone will reach the same conclusion. That obviously is not the case—as the examples above suggest. The umbrella might be protection from the sun, the request for water might indicate a need to take a pill, and a footnote may cite only one side of a controversy. Here again, the line between inference and jumping to a conclusion can be awfully thin.

Given evidence that PCB's cause cancer in people, and that PCB's are in a particular water system, all reasonable people would reach the conclusion that that water system is dangerous to people. But given evidence that there is an increase in skin cancer among people who sun bathe, not all people would conclude that sunbathing causes skin cancer. Sun bathing, they might argue, may be coincidental with exposure to other cancer causing factors.

More often than not, disagreements are based not on differences in reasoning, but in the values, assumptions, or information brought to bear. If we believe that all politicians are crooks, we will infer that a specific politician's actions are scurrilous. If we believe that politicians act for the good of all, we will look for some benefit in their actions. Either way, we will try to use reason to explain the actions. We will look for some coherent explanation as a way of making sense of things. As we saw earlier, if we can understand why someone would do something, why someone might say something, why someone might act in a certain way, we feel we have made sense of the act or statement. It's like a murder trial: if we can put together opportunity, motive, and means, we can make a case.

The more evidence we have before us, and the more carefully we reason, the more valid our inferences. This principle plays an important role with reading: the more evidence within a text we incorporate into our interpretation, the more likely we have not gone astray from any intended meaning.