The quality of being determinative; the degree to which something serves as a decisive factor or determines an outcome.
From determinative + -ness (noun suffix). This noun form extracts the abstract quality from the adjective, following productive English word-formation patterns.
When you stack suffixes like -ative and -ness, you get technically correct but nearly unpronounceable words—determinativeness is why English speakers usually just say 'how decisive something is.'
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