公共空間應該是什麼？公共空間裡的衝突該如何解決？本研究藉由中正紀念堂與街舞之經驗，歸納公共空間理論上爭論不休的問題。如何讓活動在公共空間中自由的發生？作為公共空間的中正紀念堂，代表特殊之文化意涵，與街頭舞蹈的表現的另類價值，因為硬體因素與交通區位而聚集在一起。但更重要的是街舞者如何利用生活，建構真實空間壓抑下的對立基地—第三空間，實踐公共空間真正的公共性，最終達成好的城市與好的公共空間之願景。 最後結果可以歸納為三點：第一、弱勢者在公共空間中其實一直被視而不見，因此公共空間裡需要的是真正屬於弱勢者的第三空間，否則沒有市民實踐的公共空間，沒有意義；第二、解決公共空間中的矛盾，必須回歸社會文化研究，發覺第三空間中，人、活動與次文化關係中隱含的契機—非正式體制；第三、規劃者必須有非正式體制的認知，在第三空間的社會文化與體制網絡內貢獻專業。 / What is public space? How to solve conflicts in public space? This paper has been summarized all issues of public space theory by the experience of C.K.S.'s memorial hall and street dance. How to let activities happen naturally? Public space which like C.K.S.’s memorial hall presents special cultural meaning, and combines with alternative value of street dance by material equipment and location. But more important is that how B. Boys “live” their “thirdspace” to counter pressure of real space, realize true publicity of public space, reach the goal of good city public space eventually. We can get three points in the end of this paper: first, there has be some thirdspace in public space because disadvantaged people have not been seen for so long, or public space is meaningless without people realized. Second, incase to solve conflicts in public space, we must return to social-cultural research to discover informal system, relationships between people, activities, and subculture in thirdspace. Third, planners have to realize the informal systems so to contribute their profession abilities within social-culture and network systems in thirdspace.