Specific sentences are structured to be unambiguous and self-contained.

Sentences that we speak often derive their meaning from context (the physical surroundings, or the surrounding words and sentences). For example, we might hand a book to a friend and ask "can you please put this in the bookshelf?" Based on the context, it is clear that by "this" we are referring to the book we are holding. Moreover, our friend can easily ask us to be more specific if they do not understand our request. Therefore, contextual cues are sufficient for much of our informal communication.

However, context can be much less reliable in written communication. For example, some novels have long sequences of dialogue where individual speakers are not identified. Potentially because of limits to our working memory, after several lines of text it can be easy to lose track of which character is saying which line: to lose track of the context. Therefore, readers have limits to their ability to understand sentences based on context.

For scientific sentences to be specific (unambiguous and self-contained), understanding the meaning of a sentence should not require extrapolation from context. The plain meaning of the sentence should be clear from the words of the sentence itself given definitions established in the frameworks that the sentence is part of. Clear sentences commonly share three attributes:

1) The sentence contains one main idea.

2) The subject and object of the sentence are plainly stated and unambiguous.

3) Each sentence contains all of the information necessary to understand the sentence.

1) The sentence contains one main idea.

In scientific writing, clear sentences express a single idea in as few words as possible. Sentences that each contain a single idea can be connected using logical transitions to support frameworks. For example, a student paper about academic and motor (i.e. sports activities) learning included the sentence:

"While students typically have a separate time for academics and motor learning, the question arises on which approach will meet the needs of long lasting learning and performance and whether or not massed or the spacing effect will further enhance performance."

Is the sentence clear and specific? The sentence is not specific because the sentence expresses more than one idea. A clearer construction would be to break the sentence into two sentences that each express a single idea and are connected using a logical transition:

"Students often separate academic study from motor practice. However, interleaving academic and motor practice within a practice session could result in more learning than using separate practice sessions."

Does the sentence "Childhood obesity is correlated with soda consumption" express more than one idea?

The sentence "Childhood obesity is correlated with soda consumption" might seem to express more than one idea because it contains two elements: obesity and soda consumption. However, the correlation between obesity and soda consumption is the single main idea of the sentence. Therefore, the sentence is sufficiently clear and does not require revision (although a reference would be necessary for the sentence to be a premise).

APPLICATION: Write and revise sentences to express a single idea using as few words as possible. Often, writing can be clarified substantially if compound sentences are broken into two (or more parts) connected with clear logical transitions.

2) The subject and object of the sentence are plainly stated and unambiguous.

In clear scientific writing, sentences clearly and plainly state both the subject and the object of the sentence. For example, the sentence "we measured body weight using a scale" has a clear subject ("we") and a clear object ("body weight").

Students are often tempted to write sentences where either the subject or object are determined by context. For example: "Body weight was measured using a scale. These measurements were made immediately before treadmill training."

The second sentence might seem unambiguous because it was preceded by a sentence stating that the authors used a scale to measure body weight. However, the second sentence is still unnecessarily ambiguous: we cannot be sure that "these measurements" refer to body weight. It would be clearer to simply state the subject and object unambiguously: "We measured body weight immediately before treadmill training."

Moreover, typically experiments involve many types of measurements. For example, a more realistic Methods section might include: "We measured body height while participants stood with their back against a wall. We estimated body fat using a skin fold test. We measured body weight using a digital scale. These measurements were made immediately before treadmill training." In the preceding four sentences, we cannot know whether all the measurements were made before treadmill training or not. Because the subject of the sentence is ambiguous("these"), our entire section becomes ambiguous.

Beginning the sentence with "These" results in an unnecessarily ambiguous subject. Using "These" as an object is equally confusing: "We made these measurements immediately before treadmill training." In both cases, the meaning of the sentence and the section is not clear.

A useful rule of thumb is to NEVER use ambiguous pronouns as either the subject or object of a sentence. Ambiguous pronouns include "This," "That," These," "Those," "They," and "Such."

Similar to ambiguous pronouns, ambiguous constructions include "As stated above," "As previously discussed," or other variants. Sentences that begin with a reference to a previous section of a document cannot be self-contained and therefore are NOT specific.

The most common and easy-to-spot use of ambiguous pronouns is as the subject of a sentence, where the pronoun appears as the first word of the sentence. Simply making an effort to never start a sentence with the word "this" or its relatives can dramatically improve the specificity of many people's writing.

Although not as problematic as ambiguous pronouns, constructions that obscure the subject also weaken sentences. For example, adding the constructions "It is," "There is," or "There are" at the beginning of a sentence is seldom necessary and only serves to make the subject more difficult to identify.

APPLICATION: Do NOT start sentences with ambiguous pronouns (e.g. "This," "That," These," "Those," "They") or ambiguous constructions. Do not use ambiguous pronouns as objects.

3) Each sentence contains all of the information necessary to understand the sentence.

Using ambiguous pronouns or constructions results in subjects or objects being undefined. However, students often write sentences where the object or other important information are simply absent. Without all of the information necessary to understand them, sentences are not specific.

For example, students often write sentences like "Average walking speed increased to 2.5 m/s (P<0.001)." What is the problem with the previous sentence?

The problem with the sentence is that it is missing a reference for comparison. The sentence does not indicate what value the increase is relative to. The sentence is therefore missing important information, and is not self-contained and specific. The sentence could be revised to be more specific: "Average walking speed increased from 2.2 to 2.5 m/s (P<0.001)."

When using words of comparison, it is important to include BOTH elements being compared in the SAME sentence. Without both elements being compared, sentences are not self-contained and specific. Words of comparison include:

"Increase," "Decrease"

"More," "Less,"

"Higher," "Lower," etc.

Similarly, common procedures and calculations often require more information than students provide. For example, many experiments involve more than one different condition. For example, imagine an experiment on walking speed that involved both age (young vs. elderly), vision (eyes open vs. eyes closed), and training (untrained vs. trained) conditions. Two groups (young and elderly) participants trained for one week on two walking tasks (eyes open and eyes closed). Would our sentence "Average walking speed increased from 2.2 to 2.5 m/s (P<0.001)" be self-contained and specific?

One problem with the sentence is that the sentence does not indicate the conditions that the walking speed averages correspond to. The sentence does not adequately specify the condition that the data are averaged over. As written, it is not possible to know which combination of conditions are being compared in the sentence.

A more specific sentence could read: "Average walking speed increased from 2.2 m/s before training to 2.5 m/s after training for elderly participants in the vision condition (P<0.001)." Is the preceding sentence clear and specific?

There is another problem with the sentence. One way to think about the problem is to ask the question: could we write similar sentences for our other variables, such as "Average walking speed increased from 2.2 m/s (no vision condition) to 2.5 m/s (vision condition) for elderly participants after training (P<0.001)" ? The sentence for vision is confusing because it implies that the no vision condition was measured first, and the vision condition was measured later (which wasn't necessarily the case). More generally, the words "increase" and "decrease" imply a change over a continuous variable, whereas in our example the variables "age," "vision," and even "training" are categorical data (comparing two groups).

The "age" and "vision" conditions clearly involve discrete variables that only have a finite number of values. The experiment is not testing young people as they become elderly or both young and elderly people losing their vision. Therefore, because the variables are discrete, the words "increase" and "decrease" are NOT appropriate. Better words for categorical comparisons include "more" or "less," "higher" or "lower." Therefore, the sentence would be clearer if it read: "Average walking speed was lower in the no vision condition (2.2 m/s) than in the vision condition (2.5 m/s) for trained elderly participants (P<0.001)."

What about training? Although training does depend on the continuous variable of time, the training is assessed (measured) in a discrete way and only has two values: before and after training. Therefore, even for training, our sentence would be clearer if it read "Average walking speed was lower before training (2.2 m/s) than after training (2.5 m/s) for elderly participants in the vision condition (P<0.001)."

Can we ever use the terms "increase" and "decrease?" Yes... but only clearly when there is a relationship (such as a correlation) between two continuous variables. For example, "From the years 1970 to 1990, soda consumption increased by 6% per year (Hu and Malik, 2010)."

Let's return to our walking study. Although our sentences are clearer, they are still not specific enough!

What more could we possibly need?

Extensive discussion of research methods is outside the scope of the Reasoned Writing module. However, it is helpful to keep in mind that that there are many ways to calculate averages. Often, procedures for calculating averages (and other calculations) are defined in the Methods. However, if the Methods does not clearly define all calculations, then we may need to specify the data being averaged across. For example "Walking speed averaged across the 10 training trials for each individual, then averaged across individuals, was lower in the no vision condition (2.2 m/s) than in the vision condition (2.5 m/s) for trained elderly participants (P<0.001)." Clearly, calculations that are used for many comparisons should be defined in the Methods to avoid unnecessary repetition in the Results.

APPLICATION: Specific sentences are modular: they contain all of the information necessary to understand the sentence. Sentences with comparisons require BOTH elements being compared in the SAME sentence. Calculations explained in sentences must be clearly defined in the paper or in the sentence.