" well-founded "

1: according to the rules of logic;

  * e.g., " ... even a well-founded argument can lead to an erroneous conclusion if one of the premises is incorrect "

•  Synonyms : 

•  analytic,

•  coherent,

•  consequent,

•  good,

•  logical,

•  rational,

•  reasonable,

•  sensible,

•  sound,

•  valid,

•  well-grounded

•  Antonyms : 

•  illegitimate,

•  illogical,

•  incoherent,

•  inconsequent,

•  inconsequential,

•  invalid,

•  irrational,

•  unreasonable,

•  unsound,

•  weak

2: based on sound reasoning or information;

  * e.g., " ... a well-founded complaint about the business's treatment of its customers "

•  Synonyms : 

•  commonsense,

•  commonsensible,

•  commonsensical,

•  firm,

•  good,

•  hard,

•  informed,

•  just,

•  justified,

•  levelheaded,

•  logical,

•  rational,

•  reasonable,

•  reasoned,

•  sensible,

•  sober,

•  solid,

•  valid

•  Antonyms : 

•  groundless,

•  illogical,

•  invalid,

•  irrational,

•  nonrational,

•  nonsensical,

•  nonvalid,

•  unfounded,

•  uninformed,

•  unjustified,

•  unreasonable,

•  unreasoned,

•  unsound