A logical fallacy I often observe is to witness people support the converse of an unsupported claim. Two examples:
First: embellished story- *Sara was in the car with me and some friends. One person said something like "girls are almost always late." She vigorously challenged this conclusion, asking for the evidence to support it. An example was provided. She pointed out that an anectdote is one data point and is therefore insufficient to evince a trend. She gave a counterexample of a girl being on time and said that without a statistically significant study and her approval of the study's setup, her view that girls are on time as much as men would not be upset. She manifested the typical scientist's critical questions: What are the data? How were the data obtained? What are the limits of the implications of the data?
She was right in her criticism of the claim's validity- but she was wrong to be convinced that the claim was incorrect! She should have concluded that there is insufficient evidence to say that the claim was wrong and that there was insufficient evidence to say that the claim was right. The lack of sufficient evidence should result in being undecided: not accepting the counterclaim. The evidentiary expectation of her suggestio falsi (suggestion of a falsehood) counterclaim is just as high as that of the original claim. An affirmation of falsehood must be proven; an affirmation of uncertainty need merely criticize- ei incumbit probatio qui dicit, non qui negat - the burden of the proof lies upon him who affirms, not he who denies. Affirmations of falsehood are very difficult to substantiate: compare to when Napoleon ridicules Uncle Rico's video as the worst ever. Kip replies, "Napoleon, how could anyone even know that?" Proving claims false is similarly difficult.
Second- in bioethics today we watched a star trek episode where one crew member claimed that introducing religion would inevitably lead to holy wars and inquisitions and chaos. One student challenged the claim, arguing that there wasn't enough evidence to show the inevitability of that scenario. She, non sequitur ("an inconsistent statement, it does not follow") claimed that the scenario wouldn't come to pass. Once again, showing the verity of a counterclaim is a sufficient way to debunk a claim (if an accused is innocent he or she is also definitely not guilty); but without evidence to support the counterclaim, her conclusion should have been that the dystopia might or might not occur, non constat- "it is not certain." By way of analogy to criminal proceedings, lack of evidence to convict AS WELL AS evidence of innocence both result in acquittal; only evidence of guilt, however, results in conviction. In these two scenarios, the "judge" should have concluded "not guilty" rather than either "guilty" OR the converse, "innocent." Allegans contraria non est audiendus - "one making contradictory statements is not to be heard."