Utopianism is the way of thinking that believes a perfect, or almost perfect, society can be designed and built — and, more broadly, the whole habit of imagining ideal worlds and working towards them. It names both the belief and the tradition: the books, the movements, the small communities that people actually founded to live the dream. In writing about history and politics you meet it as a label for a period or a movement, and there it is neutral: nineteenth-century utopianism, the utopianism of the early socialists, technological utopianism (the belief that machines will fix everything). But like utopian, the word very often carries a gentle warning inside it. Speakers use it to say that hope has run ahead of reality — 'the utopianism of the plan blinded them to the cost'. Karl Marx famously used 'utopian socialism' as a criticism of thinkers who dreamed of ideal villages instead of studying how society actually changes; that history is one reason the word tastes slightly critical today. It is a formal, academic word. You will read it in essays, history books and serious journalism, and almost never hear it in conversation. It is uncountable — say 'utopianism', not 'a utopianism' or 'utopianisms'. Its natural opposite in tone is realism or pragmatism, and its dark twin is dystopianism.

烏托邦主義；空想主義（相信可以打造完美社會的思想與傳統，學術書面語，常帶「過於理想、脫離現實」的評價）