The quality or state of being capable of being determined or decided.
From determinable + -ness (a suffix forming nouns of state or quality). This follows the standard English pattern of adding -ness to adjectives to create abstract nouns representing their qualities.
Adding -ness to words is one of English's most productive shortcuts for creating abstract concepts—determinableness is a mouthful, which is why we rarely use it, preferring simpler phrases like 'the ability to be determined.'
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