Specious reasoning is any argument or analysis which has the apparent ring of truth or plausibility but is actually fallacious.
Such arguments are attractive because they are seemingly well-reasoned or factual, but are either fallacious or insincere. They are deceptively pleasing, but when not honestly mistaken are based on pretense. Many specious arguments are used as support for strongly held beliefs but are false. This kind of apologetical reasoning has a deceptively attractive appearance intended to generate a favorable response. It can be beautiful, well-constructed, elegant in simplicity, pleasing to consider; appearing completely reasonable at first view, apparently plausible, right, superficially fair, just, or correct, but not so in reality. A specious person or book can be bequiling because what they present themselves to be appears to be actual reality, not imaginary. Many such people and writers have themselves been "taken in" and deceived, and they sincerely believe what they say; and it is that which makes them seem all the more plausible.
In contrast to misled, sincere reasoners and apologists, political demagogues, charlatans, con artists, and many merchants and salespeople are all specious liars. See marketing strategy and advertising.
The only defense against specious reasoning is good common sense, established physical, mental and emotional health, personal mature judgment and knowledge of human nature, an objective standard of external truth, a full and independent impartial examination of claims presented for acceptance, and a well-ordered understanding of the subject based on thorough research and the testimony of proven experts, and one's own personal knowledge and experience in that particular field of knowledge.