Apparently right; superficially fair, just, or correct, but not so in reality; appearing well at first view; plausible; as, specious reasoning; a specious argument
plausible but false; "a specious claim" plausible but false; "specious reasoning"; "the spurious inferences from obsolescent notions of causality"- Ethel Albert
Something that is specious seems to exist or be true, but is not real or true. It is unlikely that the Duke was convinced by such specious arguments. seeming to be true or correct, but actually false (speciosus , from species; SPECIES)