Defining Ideology: Theory or Practice?

It wasn't real [ideology] is a phrase that anyone who has participated in political discussions for long enough will have come across in some form or another. It is often associated with communists or socialists who will refuse to accept various dictatorial regimes as examples of their ideology, but it is not an exclusively left-wing retort - many hardline social conservatives posit that moderate conservatives are not conservatives at all (see: RINOs). While many would just dismiss such a response as a no true scotsman fallacy, it does beg the question: what defines an ideology? Is real communism, if such a thing exists, defined by the writings of Marx and Engels, or is it defined by the practice of the Soviet Union?

Personally, I believe that theory matters the most but should not be the sole source from which definitions of an ideology are defined. There are varying definitions of what capitalism is but it is commonly understood that capitalism is an economic system with markets, private property rights, and voluntary exchange. If a regime calling itself capitalist was to repudiate all of these things, would it still be capitalist? I would argue no. At the same time, I think practice does not matter. If every self-identified capitalist regime started to repudiate the fundamentals of what is theoretically understood to be capitalism, we could start to consider the theory outdated and distinguish between an old capitalism and a new capitalism.

I have been curious about this topic for some time and after lurking in another thread I decided to put this question forward for others' input.

The theory of an ideology is what you look at to see the basics - what is this ideology’s principles, what does it value, etc. The practice of an ideology is what you look at to see how it actually works in the real world (or doesn’t).

I had a heated debate once at a work meetup about what “real conservatism” meant.

We all had different takes, and things got tense until someone pointed out that focusing too much on labels can hurt social cohesion and diversity - https://sites.google.com/view/the-fracturing-effect-of-ident/ it actually made everyone step back and listen instead of argue.

It made me think that maybe theory is important, but seeing how ideas play out in practice—and how they affect people around you—matters just as much.