Long sentences: Long sentences are not necessarily difficult to understand, but writing them requires good writing skills and a strong command of the language. If either of these is absent, long sentences often end up being defective in grammar and/or structure.
Long subject‒verb distance: If the subject is separated from its verb by many words, one of two things can happen. (1) The reader focuses on the intervening text and loses track of the main sentence. (2) The reader simply scans over the intervening text while anticipating the verb in order to make sense of the sentence. This separation is particularly risky with the passive voice because the verb comes at or near the end of the sentence. This is the main reason why journals ask their authors to write in the active voice.
Long subordinate clauses: A subordinate clause contains a subject and a verb but cannot stand on its own. It is used to provide additional information but is not essential for the sentence. It is separated from the main sentence by a pair of commas or parentheses. If these clauses are too long or too many, they interrupt the sense of the sentence.
Rambling sentences: A rambling sentence usually contains several independent clauses, each of which can stand on its own like a sentence. If there are more than two such clauses they give the sense that the sentence has no end, which can be disorienting. In the following example, the colon (:) and semicolon (;) are used correctly to separate the clauses, but the presence of 3 clauses, 78 words and 8 verbs in one sentence is not a formula for clear writing.“Downstream of cadherin-bound PG, PVIgG negatively interfere with a signaling pathway that relates to terminal differentiation and involves GSK3b: the transiently enhanced turnover of Dsg3 and PG in response to PVIgG was followed by delayed terminal differentiation and consequently sustained proliferation; GSK3b inhibition was sufficient to abrogate blister formation in PVIgG-injected neonatal mice, supporting the possibility that the PVIgG-targeted signaling pathway involves the PI3K/GSK3b axis that in turn is in control of PG nuclear trafficking and consequently c-Myc.”
Verbosity: Scientific writing should be concise. But scientists favor phrases over single words that have exactly the same meaning. “Due to the fact that we observed multiple cases of hepatitis C infections ..” can be shortened by half to “Because we observed many hepatitis C infections …”
Scientific jargon: Jargon is essential for science, but it should be used for necessity rather than routinely. Journals, especially those that are for wider audiences, advise against excessive use of jargon. “Produced a higher level of protein X” is ubiquitous in the scientific literature. It simply means “produced more protein X.” “The number of cells was quantified” means “The cells were counted.”
Incorrect position of modifiers: Misplacement of adjectives, adverbs and phrases that play those roles can change the meaning of the sentence completely. In the following example the four sentences have different meanings depending on the placement of “only.”
– Only the surgeon examined Peter yesterday.
– The surgeon examined only Peter yesterday.
– The surgeon examined Peter only yesterday.
– The surgeon only examined Peter yesterday.
Series of “and” and “or”: It is legitimate to have several instances of “and” and “or” in a sentence, but unless they are ordered and written correctly the meaning becomes incomprehensible or comprehensible but wrong.
That & which: The wrong choice between “that” and “which” can flip the meaning. “We removed the tumors that were on the superior surface” would raise a question about why the tumors on the inferior surface were not removed.” Though that and which are sometimes used interchangeably in general writing, in science they should be used specifically.
Punctuation: Correct punctuation facilitates reading and clarifies the meaning. But incorrect punctuation can even change the meaning. The comical example is “Let’s eat, John” versus “Let’s eat John.” Here, our common sense saves the day, but in scientific writing incorrect punctuation can cause confusion.