Thus one might analyze how new ideas changed political discourse and the basic categories through which actors see reality, how they reflect a changed conception of legitimacy, new historical interpretations, or critical attitudes. One can look at how these new concepts were used by diverse groups of actors to forge a new conception of, and identity for, the Soviet Union. Ideas do not simply matter when they affect outcomes. They also affect how outcomes are interpreted after the fact. In this connection, it will be useful to use some language to describe the causal weight you assign to ideas.
Counterfactual claims are one useful way to clarify such causal claims.
Another helpful approach is to specify clearly what general patterns of evidence a given explanation or causal mechanism would predict. The purpose of the latter is to help define the scope of our inquiry.