This is a meta-ideology and method of truth verification. The basic tenant is that given the uncertainty of how reliable different sources of information can be, we should choose to place emphasis on when different original sources agree with each other about facts and beliefs. From this we can construct an ideological framework and possibly even a religion based on concordance.
For instance, while the details of many religions and political ideologies differ, they often share key features or ideas that perhaps hint at an underlying truth. Similarly, the scientific method can be seen as a concordance of theory with experiment.
A central notion is the democracy of ideas. That is to say, the number of people who independently believe in an idea should influence the weight given to it.
A similar notion is the diversity of ideas. More weight should be given to ideas that concord despite coming from otherwise very different sources of knowledge. In particular, ideas that are developed independently in parallel should be considered more universal.
Another notion is the test of ideas. The practical success of ideas and the people who articulate them should serve as a proxy for their accuracy. The truth flourishes because it has practical value.
Another tenet is that where there is discord there is doubt. If two viewpoints oppose or conflict with each other, it is indicative of some kind of falsehood, and should cast into doubt both sides as being incomplete in their understanding of the truth, though not necessarily proportionately. It doesn’t mean both are equally wrong, but simply that there is something wrong here.
In terms of principles, the primary one would be the equality of all beings and a preference for fairness and cooperation manifesting in voluntary agreements built on the informed consent of equals.
Certain practices that follow from the observed concordances would include belief in higher powers of some kind, and the basic notions of democracy and self-determination.