LFotW: Ad ignorantum

This week's Logical Fallicy is Ad Ignorantum or the argument from ignorance. The argument from ignorance basically states that a specific belief is true because we don't know that it isn't true. Defenders of extrasensory perception, for example, will often overemphasize how much we do not know about the human brain. It is therefore possible, they argue, that the brain may be capable of transmitting signals at a distance.
UFO proponents are probably the most frequent violators of this fallacy. Almost all UFO eyewitness evidence is ultimately an argument from ignorance – lights or objects sighted in the sky are unknown, and therefore they are alien spacecraft.

Intelligent design is almost entirely based upon this fallacy. The core argument for intelligent design is that there are biological structures that have not been fully explained by evolutionary theory; therefore a powerful intelligent designer must have created them.