English Idioms and Expressions 

Idioms: Doubt and Uncertainty
from:  'beyond a doubt'  to: 'without a shred of doubt'

• beyond a/any reasonable doubt
  • This is a legal expression which means that something is certain.
    "The court established, beyond any reasonable doubt, that the man was innocent"
    
    
• beyond the shadow of a doubt
  • If you believe something to be true beyond the shadow of a doubt, it is true with total certainty.
    "A security camera recording establishes, beyond the shadow of a doubt, his presence at the time of the burglary.
    
    
• cast a doubt
  • If someone or something casts a doubt , they cause others to view something with suspicion or uncertainty.
    "The delays in delivery cast a doubt in our minds about the reliability of the manufacturer.”
    
    
• credibility gap
  • A credibility gap is the extent of doubt concerning the veracity of something, or the difference between what a person in authority (especially a politician) promises or claims, and what the public actually sees happening or the actual facts.
    "There is a growing credibility gap between what the politician promised electors and what he claims to have achieved so far. "
    
    
• doubting Thomas
  • A 'doubting Thomas' is a person who will not believe something without proof, or without seeing it for themselves.
    "I had to show him my membership card. What a doubting Thomas!"
    
    
• have doubts about someone or something
  • If you have doubts about someone or something, you have suspicions about them or you do not trust them completely.
    "I have my doubts about the honesty of the painter. His estimate seems unusually high."
    
    
• (give someone) the benefit of the doubt
  • If you give someone the benefit of the doubt, you choose to believe that the person is innocent, honest or telling the truth, because there is no evidence to the contrary.
    "Although he found it hard to believe Tom's explanation, the teacher decided to give him the benefit of the doubt."
    "Let's give her the benefit of the doubt before accusing her. She may have a valid explanation."
    
    
• a nagging doubt
  • A  persistent feeling that something is not right that causes you to be uncertain about the exactitude or validity of something is called a nagging doubt..
    "The population had a nagging doubt about the validity of the results of the election."
    
    
• often wrong, never in doubt
  • The expression often wrong, never in doubt refers to someone who has unwavering confidence although they are frequently wrong or have previously made mistakes.
    "Harry is sure his idea will work "
    "Well, you know Harry - often wrong, never in doubt !"
    
    
• sow (or plant) the seeds of doubt
  • If something sows the seeds of doubt in a person's mind, it causes somone to have suspicions or incertitude about something.
    "The fact that the boy spent a lot of money after the burglary sowed the seeds of doubt in our minds."
    
    
• when in doubt, do nothing
  • This expression means that if the right course of action is not obvious or clear, then it is better to do nothing than to act and have regrets.
    
    
• without doubt/without a shred of doubt
  • If something is stated or proved without doubt, or without a shred of doubt, there is not the slightest uncertainty concerning its validity or truth.
    "This photo proves, without a shred of doubt, that the witness was present at the scene of the accident."