"Intense" and "intensive" are two different words:
If you are putting forth an intense effort, your work is “intense”:
“My intense study of Plato convinced me that I would make a good
leader.” But when the intensity stems not so much from your effort as
it does from outside forces, the usual word is “intensive”: “the
village endured intensive bombing.”
Is there any way to understand why the word ending in "se" has one meaning, and the word ending in "sive" has another meaning?
Best Answer
The reason these two words have different endings is because they grew from two different root words in Old French, which helped form Old (and Modern) English.
Intense came from the French word intensus, meaning "stretched, strained, tight".
Intensive came from the English word intend, which in turn came from the French words entendre and intendre (essentially the same word), which means "to direct one's attention to".
Interestingly, both of these French words have the same Latin root word intendere, which is literally "to stretch tight", but entendre took a separate path in terms of connotation and meaning and developed into the word we have now.