Subject	refraction
Predicate	has_property
Object	necessary
Modality	Modality Occurrences
Polarity	POSITIVE
Plausibility	0.6740
Neighborhood Sigma	0.7172
Local Sigma	0.6740
Example Sentences	Sentence Occurrences Source refraction is necessary 2 Google Autocomplete refraction is necessary to see clearly 1 Answers.com Questions