Use specious to describe an argument that seems to be good, correct, or logical, but is not so. We live on the earth, therefore the earth must be the center of the universe has been proven to be a specious theory of the solar system.
Specious is pronounced "SPEE-shuhs." Something that is specious is attractive in a deceptive way, and if you follow the word's etymology, you'll see why. In Middle English, this adjective meant "attractive," from Latin speciōsus "showy, beautiful," from speciēs "appearance, kind, sort." Latin speciēs is also the source of English species.