The phrase "an idea by which" is correct and usable in written English.
It can be used to introduce a concept or notion that serves as a basis for further explanation or discussion.
Example: "The proposal presented an idea by which we could improve our workflow and increase productivity."
Alternatives: "a concept through which" or "a notion that allows for".
The Belt and Road Initiative has become more than just an interesting idea by which to focus diplomatic, economic and strategic thinking, it has become instead an end in itself.
On the other hand, only passive affects are passions: "an affect that is called a Passion [pathema] of the Mind is a confused idea by which the Mind affirms of its Body, or some part of it, a greater or lesser power of existing [existendi vis] than before, which, when it is given determines the Mind to think of this rather than that" (III Gen. Def. of the Affects).
He has been treating freedom "only as a transcendental idea" by which reason is led to think of its ability to begin a series of events in the sensible world.
Mr. Bradbury referred to himself as an "idea writer," by which he meant something quite different from erudite or scholarly.
Loosely speaking, the extension of an idea is "the collection of all the objects falling under it" (Bolzano 2004, 46), but strictly speaking, it is "that attribute of an idea by virtue of which it represents just these objects and no others" (Bolzano 1973, 104).
The general idea by which the specific topoi can be characterized is rather this: Every specific topos gives us a general (but not formal) description of things that are supposed to be good, noble, just, etc.
Under all the sorrow at misjudged yearnings, it is the age-old racist idea, the idea by which, sooner or later, all empires are rationalized.
Jamie Kelsey-Fry, a supporter of Occupy London, said: "If you were to measure the power in an idea by the extent to which it is suppressed, then Occupy were articulating something profound.
We are, in other words, asked to combine the idea of art as idea with the claim that we can, as spectators, convey an entirely new and fresh interpretation onto an artwork that is nothing but an idea which, by definition, needs to be about or concerned with something.
And yet hybrid leaders tend to build their lives around a few core convictions since they have little but their ideas by which to define themselves.
