Idea
An idea was an intangible thought, opinion, or concept developed in the mind.

Individuals attempting to solve a problem would often pool their problem solving skills, asking for and offering ideas or suggestions. (; )

Ideas and beliefs
The understanding that there were certain universal ideas and concepts common to all intelligent life was the basis for the universal translator. ()

Vanna, commenting on the hazardous effects of zenite gas, was surprised "that something which is neither seen nor felt can do so much harm." Captain James T. Kirk noted, "That's true. But an idea can't be seen or felt. That's what's kept the Troglytes in the mines all these centuries, a mistaken idea." ()

Ideas as dangers
Ideas among even disbelieving audiences were considered to metaphorically spread quickly. In 2369, Klingon Chancellor Gowron was confident a  was a fake orchestrated by Koroth, but knew the idea that Kahless the Unforgettable had returned had to be stopped quickly or it would spread chaotically throughout the Klingon Empire. ()

Individuals and organizations often worked to prevent ideas they considered dangerous from spreading within their populations, such as the Kelvan belief of strange Human ideas. ()

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Philosophy