Put your points positively when you can. When readers are faced with a negative they must first imagine the positive alternative then mentally cancel it out. So clarify your meaning by using positive rather than negative vocabulary.
(1) Even single negatives can cause confusion
Vote for not more than one candidate.
Vote for one candidate only.
(2) Multiple negatives – When two, three, or more negatives are gathered together in the same sentence, meaning may become obscure.
‘Dependant relative’ includes a member’s child or adopted child who has not attained the age of 18 or has not ceased to receive full-time education or training.
‘Dependant relative’ includes a member’s child or adopted child who is aged 17 or under or is in full-time education or training.