The most common negative prefixes in English are in-, un-, non-, de-, dis-, a-, anti-, im-, il-, and ir-.
Words that take a– as a negative prefix always begin with a consonant: political - apolitical
Words that take dis– as a negative prefix may begin with a vowel or a consonant: agree - disagree; comfort - discomfort
Words that take il– as a negative prefix always begin with the letter l: legal - illegal
Words that take non– as a negative prefix may begin with a vowel or a consonant: sense - nonsense
Words that take un– as a negative prefix may begin with a vowel or consonant. able - unable
Some root words can take more than one negative prefix, but the meaning of the word is then different, depending on the negative prefix used.
disable – limited in movements, senses, or activities due to a disease or injury
unable – not having the skill or opportunity to do something
discomfort – a feeling of lack of comfort
uncomfortable – a physical feeling of slight pain
to discover – to find something out or become aware of something for the first time
to uncover – to remove a cover or top from something