Use simple words to express potentially complex ideas.

Language is complex. Concepts can often be expressed with many synonymous words. Each word  for a concept may have a distinct, nuanced meaning and sound. Poetry and literature use word choice and sentence structure to convey ineffable meanings or simply sound beautiful, e.g. to be pronounced "trippingly on the tongue." 

In contrast to poetry and literature, scientific and technical writing cannot communicate meaning through nuance. Scientific writing must communicate through plain meaning and common definitions. Therefore, a reasonable goal for clarifying scientific writing is to use the simplest words possible to express concepts. 

Technical words can help identify terms that have specific meanings and prevent confusion.

Scientific writing often involves using technical terms. Technical terms and acronyms may seem complex, and students are often frustrated when reading text with technical words whose meanings the students may not know. However, being able to define and use technical terms and acronyms is important for scientists. 

Technical terms allow scientists to use words that have a specific and unambiguous meaning. For example, the word "bug" applies to organisms in the specific order Hemiptera. However, "bug" is also used generally to refer to insects. Scientists have difficulty using words like "bug" that could easily be mis-interpreted to refer to any type of insect, and must therefore use the term "Hemiptera" to refer to the order of insects. Therefore, scientists must often use technical terms for unambiguous communication.

The LACK of technical terms can also create problems. For example, the word "efficiency" has a specific technical meaning: the amount of mechanical work produced relative to the amount of non-mechanical (e.g. chemical, thermal etc.) work input (Full, 1992). However, "efficiency" also has many colloquial meanings, causing many students to use the term "efficiency" incorrectly in scientific contexts. Without a technical term for "efficiency," both authors and readers must not only know that "efficiency" has a technical definition, but also what the technical definition is. If readers mis-interpret a technical term as having another colloquial meaning, then readers could mis-understand scientific communication without being aware of it. Technical words can therefore help identify terms that have specific meanings and prevent confusion.

Replace complex words or constructions with simple words when possible.

Scientists do NOT use technical or difficult terms to appeal to authority or try to impress anyone. In fact, using complex words may have the opposite effect and diminish people's estimation of the author (Oppenheimer, 2005). Whereas technical terms may be un-defined outside of specific scientific contexts, clear scientific writing uses non-technical words that are as simple as possible. Therefore, selecting the simplest word to express a concept is one way to help scientific writing be as clear as possible.

For example, you might have noticed that in the first paragraph I used the term "ineffable." "Ineffable" is a beautiful word that captures the sentiment that I sought to express. However, "ineffable" is not a common word, and its synonym "indescribable" might be a better choice.

Similarly many long or unusual words have simple synonyms that would be better choices for clear communication:

Complex word -> Simple word to use instead

Plethora -> Many

Congruent -> Similar

Inferred -> Concluded

Multiplicity -> Several

Efficient -> Effective

Optimal -> Good

... and many, many others. 

Similarly, many complex constructions are unnecessary and can be replaced with simple words:

Complex construction- -> Simple word to use instead

Due to the fact that...-> Because

Regardless of the fact that... -> Although

In the event that... -> When

In reference to... -> About

It is important that...  -> Should

Is able to...  -> Can

It is possible that... -> May

Subsequent to.... -> After

In congruence with... -> Consistent with

... and many, many others.

Use a thesaurus only to find simpler word choices.

If you have learned the basics of the English language, you should NOT need to use a thesaurus for scientific writing. Again, although reading and writing in specific scientific fields may require learning a specific technical vocabulary, the strongest English words for scientific writing are the most common and simplest. Therefore, if you know a simple and common word or expression, it should not be necessary to use a thesaurus to find an alternate or more complex expression. 

Use a thesaurus only if you think that you may be able to improve a sentence with a simpler, more common word or expression.

Simplicity is one key to clarity despite complexity. Using technical terms may be necessary to clearly express scientific concepts and findings. However, non-technical words should be as simple, common, and clearly-defined as possible. When revising text, try to identify potentially complex words or constructions and replace them with simpler words.