Forensic linguistics focuses on using communication as evidence. In short, it allows us to unlock the secrets of communication. The word communication includes all elements: words, body language, body movements, voice, inflections, lip shapes, blinking rates, .. ad infinitum.
An excerpt from my book, "Getting the Truth: I am D.B. Cooper," explains Forensic Lingustics:
The beauty of forensic linguistics hits you when you find the rhythm and patterns of communication. It’s like enjoying a symphony. You need to experience it.
We’re looking for changes in those patterns, but you first have to discover the patterns. The forensic linguist calibrates to the individual, identifying his or her communication patterns, then determining when those patterns change. The next step is determining what caused the change. The change could be the result of many variables, such as noise, distraction, deception, and so on. Only skill, patience, practice, and perseverance will uncover it. Absorb, absorb, absorb the evidence and information. The trained observer senses all that is there and all that isn’t there that should be. You solve the puzzle when you discover the actual cause.
Like water seeking its own level, the body relieves itself of stress, seeking calmness. The greatest stress reliever known to man is truth-telling. It’s a relief valve, a bloodletting, a purging. Nature demands it in order to begin the rebuilding process. Forensic linguists, interrogators, and investigators use that force to their advantage. We know the default is truth-telling.
As we communicate, our “attendant” examines each vehicle to compose the thought we wish to communicate. Retrieving the vehicle is very fast—it’s a millisecond, a decision. Sometimes when that vehicle appears, we want it to disappear—but it’s too late, it has already appeared. We try to send it back into the parking lot, even though it was already detected, seen, and heard and has left evidence. These are Freudian slips, parapraxes, “slips of the tongue.” Everything matters in communication. The “slip of the tongue” gives us a window into the thought process of the communicator. The intended or unintended thought(s) that caused that “slip,” illuminating that vehicle, is there for us to evaluate, to interpret.
In short, forensic linguistics requires the methodical study of each and every word, each and every communication mechanism. We seek to identify communication patterns and changes in those patterns. For example, take a look at the following statement:
“I saw him come up from the basement with a gun. He went outside and shot the gun in the air.”
That sentence makes sense and has truthful traits—the change from the article “a” in “a gun” to article “the” in “the gun” is expected. Logically, it appears as if the speaker is referring to the same gun and the same shooter. The speaker uses the active voice (I saw; He went), and the past tense (saw, went, shot). We probably know what happened. The “active voice” tells you who did what: “I threw the ball.” You have no doubt who threw the ball. In contrast, we often see, “The ball was thrown,” which is the “passive voice.” The passive voice doesn’t tell you who the actor was. Truthful people want you to know the truth. Untruthful people want you to think you are being told the truth. So, we often see deceptive people use the “passive voice.”
Accordingly, what if the speaker said this?
“I saw him come up from the basement with a gun. He went outside, and a gun was shot in the air.”
This is different. Now we don’t know which gun was shot or, for that matter, who shot the gun. In the first example, we assume (assumptions are never safe) the guy who went from the basement to the outside is the one who shot the gun. In the second example, we’re left wondering who shot the gun or what gun because the speaker changed the communication pattern. Something happened to cause the change. We know the speaker can use the active voice, as shown in the first 1.5 sentences, but he or she chooses to change to the passive voice (“. . . and a gun was shot in the air”), effectively concealing the gun used and the person who shot the gun. Something caused that change. Notice that the use of passive language forces sentences to be longer, wordier, cloudier. The active voice, conversely, provides clarity and precision. The passive voice is imprecise and causes confusion, often intentionally. Deceptive people often use the passive voice to subtly conceal knowledge, the identity of the actor, or their intent. Applying forensic linguistics will allow us to better understand what really happened. It enables us to identify changes in communication patterns and help determine why those changes occurred, ultimately leading us to understand what really happened.