A passive construction occurs when the performer of an action is not the grammatical subject of the sentence. The use of passive voice is not a grammatical error; the choice between active and passive voice is a stylistic one. However, a problem does arise when you write passively not by choice.

We write to inform and influence. When our voice wavers or is unclear, it diminishes the effect our words have on the reader. Consider this sentence: Japanese cars are manufactured with better fuel performance than American cars. That sentence is both passive and effective. While it does not identify the performer explicitly, it is obvious within the context of the statement

Next, consider this sentence: Japanese cars were determined to provide better fuel performance than American cars. This is a poorly structured sentence because it is unclear who made the determination. The determination holds a great deal more importance to the reader if a respected authority made it.

The following sentence will force readers to take notice: The US EPA determined that Japanese cars provide better fuel performance than American cars.

The next time you write, choose between active and passive voice. Do not allow the voice to choose you and thus weaken your argument.