It’s a danger inherent to complex and formal writing, and I see this mistake often while editing—and in revising my own writing. It’s the error of attributing multiple, competing causes to the main clause in a sentence. Here’s a totally fabricated example:

Small birds of prey are rather easily trained. For this reason, falconry became a popular sport for the upper classes because they had the extra funds to pursue such leisure activities.

The multiple causality arises in the second sentence. The basic formula in evidence in the above example is for this reason + [main clause] + because + [reason]. This does not violate any grammatical or mechanical rules, but the presentation is problematic. Essentially, the core of the sentence, falconry became a popular sport for the upper classes, is given two quite different causes: the ease of training the birds and the disposable wealth of the upper classes.

The multiple causality is competing because of the signal phrase for this reason, which indicates that only one cause will be identified. Almost no one would misread it this way, but the sentence is effectively suggesting that the ease of training and the disposable wealth factors are one and the same. Clearly they are not, so the sentence structure should reflect that.

For clarity’s sake, causality—whether multiple or singular—should be unidirectional and therefore noncompeting. Both of the (again, totally fabricated) reasons in the example passage could have indeed contributed to the rise of falconry as a sport, but dual causality can be better expressed:

Falconry became a popular sport for the upper classes for two main reasons: small birds of prey are rather easily trained, and the wealthy had the extra funds to pursue such leisure activities.

The multiple and competing causality could be rectified in any number of ways, but the key to nipping this writing habit in the bud is being aware of it in the first place. Simply committing to a revision process of any kind is a step in the right direction because this problem is usually a result of stream-of-consciousness writing, which we all do naturally when we are just getting ideas down on paper or screen.

The following are few signal words and phrases that you’ll want to make sure involve only unidirectional, noncompeting causality (if any causality at all). If you spy more than one of these in a sentence or adjacent sentences, take extra care to avoid the multiple, competing causality flub:

  • because
  • so
  • due to
  • as a result
  • effectively
  • therefore
  • a result of
  • determine
  • as a consequence
  • owing to
  • on account of
  • by

Remember, when I say “unidirectional,” I do not mean to suggest that only one cause can be assigned to any one effect, or vice versa. I simply mean that signal phrases work best if they point either forward or backward rather than sandwiching the cause or effect, as the example passage does.

To recap: multiple, competing causality is not a grammatical or mechanical error, but the imprecision can impede readability. In the service of clarity, present your causal statements in as straightforward a way as possible.

In a related note, remember that correlation is not causality. But that’s another topic entirely.