The Importance of Signposts in Scientific Writing
Draft 2 May 2002; revised 22 October 2002
A unit of writing is clear to you when you always know where you are,
where you are headed, and where you have been. This principle applies to
sentences, paragraphs, and entire documents; here we consider sentences. Clarity
also implies that the reader be able to get the essential meaning of a sentence
on the first pass—no going back and rereading. The reader may have to ponder
the implications of its meaning, but that is different from rereading for basic
meaning.
This “one-pass clarity” requires three
things: that the reader sense the coming and going of each structural unit while
moving through the sentence, that the reader understand each unit as it appears,
and that the reader grasp the evolving and narrowing meaning of the sentence as
it unfolds. Here we deal with only the first requirement.
The basic structural units of simple
sentences are subject, verb, object(s), and modifiers of the verb (adverbs of
various sizes and shapes). Additional units in more-complex sentences include
clausal modifiers at the beginning or end of the sentence (sometimes called
“introductory” and “concluding” elements), which may be words, phrases,
or subordinate clauses. Sentences can become more complex when these units
contain their own units, as in subordinate clauses or elaborated noun phrases.
It is easy for fiction and nonprofessional
prose to be written clearly, for they deal with everyday thoughts that can be
expressed simply. For example, the sentence “I will be on leave this Thursday
and Friday” is clear because we all know what “be on leave” means and
because the sentence is constructed simply and directly: “I [subject] will be
[verb] on leave [predicate adjective] this Thursday and Friday [adverb
phrase].” No tricks here. A more-involved sentence would be “I
am writing to you as a member of the National Association of Marine Laboratories
to ask for your help in spreading the word about this opportunity and suggesting
candidates.” It is still clear, but the units are more and longer: “I
[subject] am writing [verb] to you [adverb] as a member of the National
Association of Marine Laboratories [adverb] to ask for your help in spreading
the word about this opportunity and suggesting candidates [long adverb].”
It is equally easy for scientific and
technical writing to be written unclearly, for they deal with difficult topics
that are often convoluted and out of the realm of ordinary experience for many
readers. The units of expression are often longer and more detailed, and move in
directions that readers cannot anticipate. That means that scientific and
technical writers need to help their readers as much as possible. They can do
this by (1) keeping the structure of sentences as straightforward as possible,
(2) making the units of expression as recognizable as possible, and (3)
providing cues when moving from one unit to the next. The more difficult the
prose, the more its writer must help the reader.
Here is an example of a technical sentence
that works: “Ecological systems everywhere are threatened by climate change,
acidic deposition, ozone depletion, nonpoint pollution, and habitat
alteration.” It works for three reasons. First, it starts simply and directly,
with short and obvious subject and verb that are next to each other:
“Ecological systems everywhere [subject] are threatened [verb].” Second, it
places its elaboration at the end, as a single prepositional phrase (that
modifies the verb): “by climate change, acidic deposition, ozone depletion,
nonpoint pollution, and habitat alteration.” Third, it keeps the structure of
each compound prepositional object of the elaboration as short and nearly
parallel as possible: “by climate change, acidic deposition, ozone
depletion, nonpoint pollution, and habitat alteration.” Note
how each of the five objects has two words, an adjective followed by a noun. No
surprises here. Compounding is like climbing stairs—the first step establishes
the expectation for the next ones. If the second or third step differs from the
first, you may stumble or fall—if the second or third compound element has a
different structure from the first, you will be surprised and will have to pause
for a moment to adapt to the difference. The wise writer does not force the
reader to deal with nonparallel compounding.
The simple structure of this sentence can
be seen below, where increasing indentation means smaller scale, or narrower
focus:
Ecological
systems everywhere
are threatened
by
climate change, acidic deposition, ozone depletion, nonpoint pollution, and
habitat alteration.
Showing the compound prepositional objects in parallel makes the sentence look like this:
Ecological
systems everywhere
are threatened
by
climate change,
acidic deposition,
ozone depletion,
nonpoint pollution,
and
habitat alteration.
Of course, not every technical sentence can be constructed as simply as
this one, but we should keep this kind of simplicity as our goal.
Here is a technical sentence with more
levels of structure: “EMAP has become an integrated federal program that
provides monitoring data for assessing ecological risks and helping decide how
best to manage and protect the environment.” Any reader who does not already
know about EMAP will probably have to slow down near the end of the sentence to
sort out its various levels. The strength of this sentence is that it starts out
simply and forcefully with a simple subject and verb right next to each other:
“EMAP [subject] has become [verb]…” It then continues with a subject
complement (“an integrated federal program”) that is short and clear until
you realize that there is more to it: “an integrated federal program that
provides monitoring data for assessing ecological risks and helping decide how
best to manage and protect the environment.” The simplest structure of the
entire sentence looks like this:
EMAP
has become
an
integrated federal program
that provides monitoring data
for
assessing ecological risks
and
helping decide how best to
manage
and
protect
the
environment.
That’s eight levels of structure, six of them following
the verb. This sentence works in spite of all its levels because it keeps the
individual elements short and clear, and the two parallel structures (the
compounds) truly parallel. Violate any of these conditions, though, and the
sentence would stop working.
Here is an example of a sentence with a
subject that is long enough to need the kind of signposts usually reserved for
full sentences: “The import of increasing CO2 during the 20th
century and the projected increases during the 21st century becomes
more apparent when shown with trends over the past 150 thousand years.” When I
read this sentence, I think I have read a plural subject (“The import of
increasing CO2 during the 20th century and the projected
increases during the 21st century”), and so I expect to see a
plural verb. Instead, I see the singular “becomes.” That jars me, and I have
to return to the beginning and reread to find why the subject is singular (or
whether it should really be plural). In structural terms, I grouped the parts of
the compound subject as follows:
The import
of increasing CO2 during the 20th century
and
the projected increases during the 21st century
That is a plural subject. The writer, however, intended for the subject to be grouped this way:
The import
of
increasing
CO2 during the 20th century
and
the
projected increases during the 21st century
Why did I misread the writer’s intent? There must have been some solid reason, for I misread this sentence several times in a row. The “right” and “wrong” groupings shown above reveal the reason—the writer misplaced a “the” and so created a false parallelism that threw me off. Parallel constructions must be written in strict fashion if they are to work properly. Look at how the “the” after the “and” creates a second element nearly parallel with the first (highlighted here for emphasis):
The
import of increasing CO2 during the 20th century
and
the projected increases during the 21st century
It almost forces you to read the
phrase wrongly.
Luckily, the problem is easy to fix as
soon as you realize that the first one or two words of the parallel elements
establish most of the parallelism. You make the two parallel elements properly
parallel by adding a “the” before “increasing” or remove the one before
“projected. Here is the one with the added “the”:
The import
of
the
increasing CO2 during the 20th century
and
the
projected increases during the 21st century
Here is the version with the deleted “the”:
The import
of
increasing
CO2 during the 20th century
and
projected
increases during the 21st century
But we’re still not quite there, for the two “parallel” elements are not yet fully parallel—note the jarring “increasing” in the first and “projected” in the second.” We need to make both words “—ing” or “—ed.” I think “—ed” makes more sense, for “projected increases” is more reasonable than “projecting increases.” That change gives us:
The import
of
increased
CO2 during the 20th century
and
projected
increases during the 21st century
The entire sentence then reads: “The import of increased CO2
during the 20th century and projected increases during the 21st
century becomes more apparent when shown with trends over the past 150 thousand
years.” It is now completely clear, at least to me.
The moral? Little words can count for a
whole lot, especially in constructions as easily degraded as parallelisms. Keep
your parallelisms strict and your eyes alert for possible misunderstandings.
[At this point I thought I was finished
with the sentence. Then I noticed that it still wasn’t fully parallel, for it
contained “increased CO2” in the first element and
“increases” in the second element. Better to make them both “increases”:
The import
of
increases
in CO2 during the 20th century
and
projected
increases during the 21st century
The full sentence then becomes
“The import of increases in CO2 during the 20th century
and projected increases during the 21st century becomes more apparent
when shown with trends over the past 150 thousand years.” NOW we are finished.
The second moral, “When you think you
are finished, check again. You may not be.”]
Here is a sentence that is unclear because
it lacks certain critical signposts about its structure. As with many such
sentences, it can be fixed easily as soon as the reason for the unclarity is
recognized to be structural: “For each estuary, replicate freshwater flushing
times were calculated using the average freshwater flow rate into each estuary
including the POTW input into NB harbor for two successive 11 month periods, the
estimated average salinity at the same average flow rate (see Figure 5), the
estimated estuary volume and a constant boundary salinity.” I daresay that
nearly anyone reading this sentence for the first time will be lost by the
middle—I certainly was.
Here is the underlying structure of this
sentence:
For
each estuary,
replicate freshwater flushing times
were
calculated
using
the average freshwater flow rate into
each estuary
(including the POTW input into NB harbor) [parentheses
added]
for two successive 11 month periods,
the estimated average salinity at the
same average flow rate (see Figure 5),
the estimated estuary volume
and
a constant boundary salinity.
That’s six levels of structure, one fewer than
successfully handled in the previous example. Why is this sentence so much
harder to read?
The answer lies in a combination of
several simple factors. First, the writers introduced an unnecessary level of
structure by beginning the sentence with a clausal modifier “For each
estuary”) that also buried the subject by postponing it. Given the length of
the sentence to come, it would have been better to make the introductory element
part of the subject: “Replicate freshwater flushing times for each
estuary…” Second, the writers inserted the parenthetical element
“including the POTW input into NB harbor” but did not indicate its
parenthetical (nonrestrictive) nature by parenthesizing it or setting it off by
commas (the former being preferred because of the number of commas already
present in the sentence). They wrote the confusing “using the average
freshwater flow rate into each estuary including the POTW input into NB harbor
for two successive 11 month periods” when parentheses would have clarified
their meaning instantly: “using the average freshwater flow rate into each
estuary (including the POTW input into NB harbor) for two successive 11 month
periods…” Third, they allowed the last two of the four compound objects of
“using,” namely “the estimated estuary volume” and “a constant
boundary salinity,” to become confused because they omitted the serial comma
after the third one. The serial comma would have removed any ambiguity at the
end of the long participial phrase, and would have allowed the final two
elements to read: “the estimated estuary volume, and a constant boundary
salinity.” This would have removed any question as to whether the boundary
salinity had been estimated. (It wasn’t.)
The restructured sentence (with a couple
more minor revisions) reads:
Replicate
freshwater flushing times for each estuary
were calculated
from
the average freshwater flow rate into each estuary
(including the POTW input into NB
harbor)
for
two successive 11-month periods,
the estimated average salinity at the same average flow rate (Figure 5),
the estimated estuary volume,
and
a constant boundary salinity.
We need not stop here, however. We can make the sentence read better by beginning that series of four elements with the shortest and ending with the longest, as long as no important scientific sequence is violated. The reason for doing this is to ease the reader into the sequence and use the shorter initial elements to establish the pattern as comfortably as possible. The rearranged sentence might read something like this:
Replicate
freshwater flushing times for each estuary
were calculated
from
a constant boundary salinity,
the estimated estuary volume,
the average freshwater flow rate into each estuary
(including the POTW input into NB
harbor)
for
two successive 11-month periods,
and
the estimated average salinity at the same average flow rate (Figure 5).
This sequence also gives the reader a chance to pause
briefly after the long third element. Written out as a sentence, it would now
look like this: “Replicate freshwater flushing times for each estuary were
calculated from a constant boundary salinity, the estimated estuary volume, the
average freshwater flow rate into each estuary (including the POTW input into NB
harbor) for two successive 11-month periods, and the estimated average salinity
at the same average flow rate (Figure 5).”
The moral of this little exercise is that
the clarity of scientific sentences can often be dramatically improved by adding
simple signposts to structure such as parentheses and commas. Little cues to
structural elements can go a long way.