Reply #8: But you can strip it of its effectivity to the point of non-existence

[alcibiades_mystery]

Ideas are something like viruses. Smallpox is technically "still around," but its capacity to affect people is greatly diminished, almost to the point of its non-existence. This does, in fact, happen to ideas all the time. Whether an idea is "alive" or "dead" is therefore inconsequential - a nice little conceit on the part of the writers, but ultimately meaningless in practice. Ideas require the capacity to "infect a host," to keep the metaphor running, and that capacity CAN be attenuated. An idea without its corresponding wetware is "dead" for all practical purposes.

(Just as a note, this is what Nietzsche meant when he said "God if dead." He was not, obviously, referring to an actually existing God who had somehow "died." Rather, he was referring to the "idea" or concept of God as it circulated and affected society and thought in "pre-Enlightenment" Europe. So, the "idea" of God as foundation for, say, ontological and ethical claims had "died" - it had lost its capacity to affect society and thought in the same way it had in the past)