In science, it is especially important to write so readers can easily get the intended meaning. With non-scientific prose, an author's intended meaning may not be immediately obvious, but not getting it usually doesn't result in insurmountable confusion like it can in science. We can figure out what is meant by "Toys R Us" or even "Are team is the best." But when readers of a scientific article stop to guess the author's intended meaning, confusion is likely and disaster is possible -- even when the intended audience is only the few people working in the author's own area.
Science can be complicated. For clear scientific communication, it often seems necessary to present two or more ideas simultaneously. This isn't possible given the limitations of language, primarily its linearity. But authors can deal with the problem by using sentences with dependent clauses. Authors can also present more than one idea simultaneously using boxes or hyperlinked text, but readers still will encounter the material in a sequential way. So authors often rely on old-fashioned multi-clause sentences -- enlisting every tool available. The correct use of which and that is a powerful tool that helps readers distinguish one sort of meaning in dependent clauses from another; accordingly, it doesn't make sense to disregard it.
Scientists who make use of the distinction between which and that benefit in three areas.
Correct use of which and that allows writers to give more information with fewer words, with clarity, precision, and less ambiguity. These two sentences with different meanings serve as examples:
"We labeled the DNA that was synthesized between ten and twenty minutes after infection." This implies that DNA may be synthesized at other times, but we labeled only the DNA synthesized in that particular interval.
A second reason to try to use which and that correctly is there is a good chance a copyeditor will change the meaning of a sentence. Consider the following example:
All molecules which are drugs bind to receptors.
The author has (incorrectly) used which to introduce a restrictive clause that describes a subset of molecules -- drugs. The copyeditor (who doesn't know about molecules but does know about the rule of grammar requiring nonrestrictive clauses introduced by which to be separated from the rest of the sentence by commas) adds commas and gets a factually incorrect sentence saying all molecules are drugs:
All molecules, which are drugs, bind to receptors.
Another reason to recognize the distinction between which and that is to avoid sounding pompous, pretentious, or uppity. The impression that the excessive use of which can leave sometimes hinders effective communication.
If you want to see an explanation of the correct use of which and that -- with set theory and Venn diagrams -- especially for scientists, go to The Distinction Between Which and That.
If you want to know what makes me think I'm qualified to write about the distinction between which and that, go to How I Became Qualified to Write on this Topic.
© 1998 by Lorraine Lica