Based on the input-output pairs, I can provide an approximation of the concept(s) that f(x) is selective for.

[DESCRIPTION]: The function f(x) appears to be selective for the concepts related to emotions, nature elements, and contrasting pairs. Words that are related to emotions, such as happiness, sadness, love, and joy, demonstrate higher values closer to 1. Similarly, contrasting pairs, such as light and dark, also yield high values. Additionally, words associated with nature elements like water, fire, and ocean, seem to have an association with the intended concept(s).