Right now, it seems that "passionate love" is measured in a discrete scale based on answers to a questionnaire. The "Passionate Love Scale" (PLS) is mentioned in this blog post and was introduced by this article in 1986.
In my other reply to my original comment I showed a study%20Reduced%20cognitive%20control%20in%20passionate%20lovers.pdf) that finds that "high levels of passionate love of individuals in the early stage of a romantic relationship are associated with reduced cognitive control", in which they use the PLS.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
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