佛經中有兩句話，「色不異空，空不異色」是什麼意思？
Somewhere in the Buddhist scriptures, it says "Rūpa (matter) is none other than suññatā (emptiness). Suññatā is none other than rūpa." What does this mean?
這就是說一切法「緣起性空」。「色」，就是色、受、想、行、識五蘊中的色，是指物質。任何物質現象都是緣起，它有相狀，它有功用，但是它的相狀和功用裡面沒有常恆不變的指揮它的主宰，所以說是空。所謂空，不是指的色外空（物體之外的空），也不是指的色後空（物體滅了之後的空），換句話說，並不是離開色而另外有一個空，而是「當體即空」。色是緣起所起，色法上不能有個不變的實性，所以說「色即是空」；唯其沒有實性，所以能遇緣即起，所以說「空即是色」。這也就是「色不異空，空不異色」的簡單解釋。
It just means that all dhammas are suññatā by nature according to Dependent Origination. "Rūpa", meaning matter or substance, is one of the five aggregates, namely, rūpa, vedanā, saññā, saṅkhāra and viññāṇa. Every material phenomenon is a product of the combination of causes and conditions. Though it has its own form and functions, it has no perpetual and unchangeable entity inside as its dominator. Hence it is empty. This emptiness does not refer to the empty space beyond matter (or the emptiness outside an object), nor does it refer to the emptiness after existence (or the emptiness after the extinction of an object). In other words, emptiness is not apart from matter, but "the object itself is empty." Now since matter arises according to the law of Dependent Origination, it can't possess an unchangeable material existence in each material object. Hence "matter is no different from emptiness". And since dhammas have no material existence, it can arise upon the meeting of adequate conditions. Therefore, "emptiness is no different from matter". This is a simple interpretation of the phrase "Rūpa is none other than suññatā, and vice versa".
受、想、行、識等精神現象也同樣的是緣起性空。「緣起性空」是宇宙萬有的真實相狀，即所謂「諸法實相」。大乘佛教以實相為法印，稱為「一法印」，一切大乘經教，都以實相的道理來印證。如前面所說「無住涅槃」和「菩薩六度四攝」等教義，都是以緣起性空的理論為基礎的。
Likewise, spiritual phenomena such as vedanā, saññā, saṅkhāra and viññāna are also emptiness by nature, for they also arise from Dependent Origination. Emptiness, on the basis of Dependent Origination is the true nature (lakkhaṇa) of all that exists in the universe, i.e. the reality of all dhammas. In Mahāyāna Buddhism this reality is regarded as the impress or seal of truth. This doctrine is called the "One Seal of Dhamma". All Mahāyāna doctrines are corroborated with this "One Seal". The aforesaid Buddhist doctrines—"active nibbāna" (appaṇihita-vihāra-nibbāna) and Bodhisattas' "Six Perfections" (Pāramitā) and "Four all-embracing virtues"— are all on the basis of the theory of Emptiness by nature in terms of Dependent Origination.
來源：《佛教常識答問》趙樸初
Source: Answer to Common Questions
about Buddhism, by Zhao Puchu
翻譯：趙桐
Translated by: Zhao Tong
審譯：柯馬凱
English Editor: Michael Crook
校對：北京龍泉寺翻譯中心
Proofread by: Beijing Longquan Monastery Translation Center