To provide not enough constraints to specify a unique solution.(verb)
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Use "underdetermine" in a sentence
"Just as content underdetermines force and force underdetermines content; so too even grammatical mood together with content underdetermine force."
"Generalizing, we might say that just as points underdetermine equations, so facts underdetermine theories."
"In this section, I will set aside features (i) and (ii) as being characteristic of any empirical domain: the data are always finite, and they always underdetermine one's theory."