Dangling modifiers
A modifier dangles if the implied subject of an introductory clause or phrase differs from the actual subject.
Dangling gerunds
Below are examples of dangling gerunds (gerunds are similar to participles in that they end in ing, but gerunds act as nouns rather than as adjectives - in these examples, the gerunds are objects of prepositional phrases).
example: While drinking gerund our coffee, the lions approached our camp. The implied subject of drinking is 'we' or 'whoever' is in camp, but the actual subject is the 'lions'. Correct this by making 'we' the implied subject and actual subject - While drinking our coffee, we saw the lions approach our camp or by converting the gerund phrase into a clause - While we were drinking coffee, the lions approached our camp.
example: After reviewing gerund the data, it was concluded that the experiment was poorly designed. The actual subject of reviewing is it, but the implied subject is whoever reviewed the data - After reviewing gerund the data, the panel concluded that the experiment was poorly designed.
example: Before sampling gerund the extract, pH was determined.Clarify this as before - Before sampling the extract, we determined its pH or Before the extract was sampled, pH was determined.
example: By having gerund the subject perform an action, instead of receiving gerund an action as in the passive voice, the purpose of the sentence is clearer. The implied subject for having and receiving is either the writer or the sentence but is not the purpose. So, having and receiving dangle. By having the subject perform an action, the writer clarifies the purpose of the sentence.
Dangling present participles (these present participial phrases are acting as adjectives)
example: Preparing present participle the samples, the experiment continued. (Preparing present participle the samples, the researchers continued the experiment.)
example: Using present participle positive and negative controls, convincing data were collected. (Using present participle positive and negative controls, the researchers collected convincing data.)
example: The specimens were examined using present participle a light microscope. (The specimens were examined with a light microscope.)
Dangling past participles (past participles usually end in ed)
example: Trained past participle in soil ecology, the research team's approach emphasized bacteria and fungi. The implied subject of trained is research team, not approach. (Trained past participle in soil ecology, the research team emphasized bacteria and fungi.)
example: Surprisingly, the molecular systematics of Mysticeti [a suborder of whales] have received little attention. Although generally thought past participle to include only 10-12 species, questions remain about the systematic relationships within this suborder. The implied subject of the past participle thought is suborder - it is the suborder that is thought to include - but the subject of the independent clause is questions. (Although generally thought past participle to include only 10-12 species, this suborder may contain many more.)
example: This course provides an introduction to air pollution problems grounded past participle in physical and chemical fundamentals. The implied subject of the past participle grounded is introduction, not problems. Also note the ineffective contrast of air pollution and grounded.
I was unaware that infinitive phrases could dangle until an editor pointed this out to me. The problem is the same as with dangling gerunds and participles: the phrase introduces an action that should be linked to an actor, an actor who should appear as the subject of the following clause. The infinitive dangles or is poorly attached if the subject of the following clause is someone or something who did not do the action in the infinitive.
example: To determine whether pH changed through time, soil was sampled monthly. The actual subject of the main clause is soil but the implied subject is whoever was determining soil pH.
Dangling infinitives are very common in scientific writing because scientists often use passive voice to describe methods; the actor implied by the infinitive simply dissappears in the passive voice clause. Dangling infinitives are so common that few would recognize them as being wrong, and many would argue that they are not wrong, that the sentence form (infinitive plus passive voice) is now standard in scientific writing and that the infinitive invokes an actor but does not require that the actor be explicitly named.
The easiest way to correct a dangling infinitive is to use active voice.
example: To determine whether pH changed through time, we sampled the soil monthly. But first person/active voice can be jarring if the paper has not used first person and if the Methods are mostly in passive voice. Perhaps this is yet another reason to use more active voice and more first person in scientific writing.
How about relocating the infinitive phrase? Soil was sampled monthly to determine whether pH changed through time. According to the staff at the Chicago Manual of Style, relocation doesn't help, i.e., the infinitive still dangles.
Other solutions are problematic.
Changes in pH through time were determined by sampling soil monthly.
For determining changes in pH through time, soil was sampled monthly.
As I indicated, dangling infinitives are very common in scientific writing. If I indicate that your paper contains dangling infinitives, you could decide to leave them as they are, especially if they are in the Methods section or if they otherwise concern methods. Few reviewers, editors, and readers will consider them a problem. Still, you should recognize them and understand how to change them if you want to or if you are forced to by an editor.
Update: On 21 November 2010, I was consulting the 7th edition (2006) of Scientific Style and Format: the CSE Manual for Authors, Editors, and Publishers, which is published by the Style Manual Committee of the Council of Science Editors. This book is considered authoritative with respect to scientific writing. I came upon the following dangling infinitives:
Page 145: To avoid potential confusion about the meaning of the comma, the following style is recommended. (on page 145)
To facilitate prompt binding of the issues of a volume, the title page, the volume table of contents, …., are usually published as the end pages of the last issue of the volume. (on page 448).
Summary
As always, our emphasis here is on clarity rather than on grammatical correctness. In most of the above examples, the dangling elements will distract and or slow the attentive reader. He or she will be able to decipher the sentence, but they will have to work more than necessary. To decide whether an element is dangling, read your sentences as an attentive reader would.
Some dangling participles have become standard and are no longer considered dangling. See Garner (A Dictionary of Modern American Uses) for more examples and explanation of 'acceptable danglers'.
example: Assuming the equipment arrives, the experiment will continue.
example: Considering the significance of the data, the experiment will be repeated.
example: Regarding the experiment, proper controls will be included.
example: According to the methods section, the experiment lacked a control.
