Why is ideology like a prism?

Why is ideology like a prism?

Webster says a prism is 'a medium that distorts, slants, or colors whatever is viewed through it'.

It appears to me that Marx was the first great thinker to have coined the word 'ideology'. Ideology is a distinctive form of reasoning about the individual and about the individual in society. Ideology is a systematically biased mode of thinking. Ideologies vary extensively in so far as the idioms used, the extent of bias, the degree of sophistication, the manner in which bias permeates various aspects of theory, and so on.

While ideologies vary widely in certain aspects all ideologies share some common characteristics. An identifiable logical structure is shared by all. This structure includes: 1) a moral dimension, 2) it is biased toward a specific group and is biased against those out side this group, 3) an ideology cannot not directly defend it self because it rests on assumptions that have never been critically examined or even formulated, and 4) Marx believes these assumptions to be 'nothing more than the intellectual 'transcripts' of the conditions of existence of the social group whose point of view it reflects'.

Like viewing the world through a prism, the ideologue experiences the world in a distorted manner. 'What a man does not transcend in reality, he cannot effectively transcend in thought either. The limits of his existence are the limits of his thoughts. His basic assumptions are therefore ultimately nothing but his conditions of existence 'reproduced' in thought.'

Quotes from Marx's Theory of Ideology Bhikhu Parekh