'source' vs 'driving force'

The legacy of Eugene O'neill, a towering figure in the history of American theater, is best understood as a portfolio of unforgettable families of characters. Early in his career, O'neill had derived a lesson from the acient Greeks: The family is one of the most fertile grounds for tragedy. Indeed, conflicts between family members serve as the mainspring for O'neill's greatest plays, such as Mourning Becomes Electra.

Q. The word mainspring most nearly means...
a. source
b. driving force
c. chronology
d. contradiction
e. limitation

I chose 'source,' but OA is 'driving force.' However, I don't understand why 'source' is wrong. Please tell me why.
  • A mainspring is a tight spiral of metal inside a mechanical watch or other timekeeping device. It is wound tightly and then gradually unwinds, driving the mechanism of the watch.

    In other words, it is the driving force of the watch, just as family conflict is the driving force behind many of O'Neill's plays. The plays may also have their sources - that is, their points of origin - in family conflict, but the question is not asking about point of origin; it is asking about the thing that moves the entire drama forward, just as the mainspring of a watch drives the watch mechanism forward. I suspect that's why "source" is not considered a correct answer.


    Senior Member
    English (UK then US)
    Source can fit in the sentence but it does not mean the same thing as mainspring. The mainspring of a clock (and particularly the tension in it - hence the metaphorical use here to echo the "conflict" word earlier in the sentence) is the driving force of the mechanism - the clock will not move forward and work correctly without being driven by the pent-up energy in the mainspring. So "driving force" is a much better fit to substitute for "mainspring". The plays are driven forward by the pent-up energy oof the conflicts.
    Family conflicts may have been the source of inspiration for some of his plays, but that does not capture any meaning of the energy and tension involved in the original sentence where "mainspring" was used.
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