When you wish to refer to something that serves to prevent, which is the correct adjectival or noun form, preventative, or preventive? The latter word is more commonly cited, appearing by a ratio of three to one, but the longer variant is also widely employed, and with increasing frequency. Might, however, does not necessarily make right. So, which one is better?
Both words date back to the 1600s, and the latter predates the former by a mere several decades. It retains the upper hand, however, for two reasons: First, the extra syllable is superfluous, and second, it is supported both by quality as well as quantity: The most respected publications favor preventive, while preventative is more likely to appear in print and online sources with less rigorous editorial standards. That’s a good enough reason to favor preventive.
What about similar word pairs such as exploitative and exploitive, which both refer to underhandedly using someone or something to one’s advantage? Like preventative and preventive, the first attestations of these words are only a few decades apart, though they are much more recent coinages; exploitative goes back only to the late nineteenth century, and exploitive is less than a hundred years old. But there’s a significant difference between this word pair and the previous one: In this case, the longer form is widely considered the standard, and exploitive is the inferior alternative.
Fortunately, the correct form of most words ending in -ive is obvious, as with cumulative, formative, and representative. But other endings can confuse, such as with the question of whether to use orient or orientate as a verb. In this case, each refers to facing the east, though only orient correctly applies to other references to setting or directing.
Likewise, there is the case of systematic and systemic, both of which are valid terms, but with mostly distinct senses: Though both terms obviously pertain to systems, only systematic also refers to classification and to coherent, methodical, thorough procedures. Systemic generally connotes only biological systems and is neutral in value, as opposed to the qualitative senses of systematic.
In summary, as a careful writer, research proper usage for word endings in order to avoid employing the incorrect of two similar words or a less favored variant.