공의 사상은 원시불교의 `제행무상`이나 `제법무아`라는 관념을 받아들인 사상이다. 空思想은 『아함경』이나 아비다르마 불교에도 있지만 이 空思想을 더욱 심화시켜 존재하는 모든 것의 본성은 空이라 하고, 법이 空함과 법에 자성이 없음을 분명히 했던 것은 『금강경』이다. 『법화경』에 나타난 空사상은 『반야경』의 空사상을 기반으로 하여 제 14 「안락행품」, 제 16 「여래수량품」, 제 4 「신해품」, 제 5 「약초유품」그리고 제 10 「법사품」에 나타나 있다. 제 10 「법사품」을 제외한 모든 品들은 『반야경』의 空사상을 계승한 것으로 이해 할 수 있다. 「법사품」에서는 법사(dharma-bhanaka)를 `如來使, Tathagata-duta`로 부르고 보살을 가리키는 것으로, 보살이 호지할 `홍경삼궤(弘經三軌)`를 제시하고 있다. `홍경삼궤`란 법사가 여래의 방(室)에 들어가 여래의 옷(衣)을 입고, 여래의 자리(座)에 앉아 두려워 말고 법을 설하는 것을 말한다. 여기에서 말하는 방(室)·옷(衣)·자리(座) 등은 자비(慈悲)·인욕(忍辱)·공성(空性) 등을 가리킨다. 『법화경』에 나타난 空思想의 극치는 `홍경삼궤(弘經三軌)`를 존중하여 신앙의 중요한 요소로 주창하였다는 점일 것이다. `홍경삼궤`의 주장으로 인해 경전의 受持·讀·誦·解說·書寫를 권장하는 풍조가 생겼다. 『법화경』의 제 2 「방편품」에서는 空을 우주의 통일적인 진리로서의 `일승묘법`으로 적극적으로 표현했다. 이 사상은 뒤이어 `일체중생 실유불성(一切衆生 悉有佛性)`의 여래장(如來藏) 사상이 생겨나는 단초가 된다. 『법화경』에 나타난 空사상을 체계화하여 연기(緣起)나 중도(中道)·이제(二諦) 등을 空의 입장에서 조직했던 이가 용수(龍樹, A.D.150-250)이다. 그리고 이 계통이 중관학파로 발전한 것이다.

The two key words which occur on almost each page of the Mahayana writings are Bodhisttva and emptiness. What then means first of all Bodhisattva? Buddha is the one who is enlightened. Bodhisattva means literally an Enlightenment-Being. He is a Buddha-to-be, one who wishes to become a Buddha. The Bodhisattva in this sense strives for reaching the perfect Enlightenment not only for himself, but also for other sentient beings with the skill in means, through which the latent seeds of enlightenment in others can be brought out and mature. The following ist the famous passage from the Diamond Sutra illustrating this point: Here, O Subhuti, a Bodhisattva should think thus: "As many beings as there are in the universe of beings-be they egg-born, as born from a womb, or moisture-born, or miraculously born; be they with born, or without; be they with perception, without perception, or with neither perception nor no-perception-as far as any conceivable universe of beings is conceived; all these should be led by me into Nirvana, into that realm of Nirvana which leaves nothing behind. And yet, although innumerable beings have thus been led to Nirvana, no being at all has born led to Nirvana. And why? If in a Bodhisattva the perception of a `being` should take place, he would not be called an `enlightenment-bing`." Bodhisattva is a being having the two contradictory forces of wisdom and compassion. In wisdom, he sees no sentient beings at all; in compassion, he is full of firm resolve to save them. The ability to combine these contradictory forces makes him to stay in this world and to practice Bodhisattva-Path, thereby saving himself and others. Bodhisattva, the Sutra tells us, should cultivate these two things, with the thought: "I will never abandon all sentient beings notwithstanding the fact that all things are empty." We must now make an effort to understand this important idea of Emptiness. Here the meaning of the sanskrit word sunyata deserves to be interpreted as a synonym of Non-Self. For Buddhists, emptiness is a term for the absence of self, or for self-effacement. Emptiness is that which stands right in the middle between two extremes: affirmation and negation, existence and non-existence, eternity and annihilation. Tathagatas teach the Dharma of the middle to be free from both extremes. This Dharma is now called emptiness. The following famous passage from the Diamond Sutra illustrates this point well: The lord said: "Wherever there is possession of marks, there is fraud, there is fraud, wherever there is no-possession of no-marks there is no fraud. Hence the Tathagata is to be seen from no-marks as marks." From the other point of view, the emptiness is called Suchness (tathata), because the emptiness is realized, when the real nature of the thing is seen, without superimposing any ideas upon it. At the level of the world of conventional Truth, the Lotus Sutra appears to accept the Madhyamaka doctrine of emptiness. A world where spiritual progress is paramount, truth very often depends upon context. Here is a very famous passage from the XIV chapter (安樂行品) of the Lotus Sutra to illustrate this point: Further, a Bodhisattva Mahasattva looks upon all phenomena as emptiness. He sees them duly established, remaining unaltered, as they are in reality, not liable to be disturbed, not to be moved backward, unchangeable. It is existing in the highest sense of the word, having the nature of space, escaping explanation and expression by means of common speech, not born, composed and simple, aggregated and isolated, not expressible in words, formless, really without existence, innumerable infinite, independently established, unrestrained, only existing by causes, and manifesting themselves owing to a perversion of perception. The IV chapter(adhimukti-parivarta, 信解品) of the Sutra reads: "All is emptiness, non-form, and non-action." The V chapter(Osadhi-parivarta, 藥草喩品) of the Sutra also speaks: But the Thus Come One(如來) knows that this is the Law of one form, one flavour, namely, the form of emancipation, the form of separation, the form of extinction, the form of ultimate nirvana, of constant tranquility and extinction, which in the end finds its destination in emptiness(終歸於空). The feature of laudatory self-reference, a characteristic of early Mahayana Sutras, is very much to the fore in the Lotus Sutra. If a person hears just one verse of the Sutra and rejoices in it for even a moment, the Buddha predicts that person to realize the Perfect Buddhahood. The Sutra should be not only recited and promulgated, but it needs to be worshipped, as if it were the Buddha himself, with "sundry-offerings of flower perfume, necklaces, powdered incense, perfumed paste, burnt incense, silk canopies and banners, garments or music." Those who preach the Sutra will themselves see the Buddha-the Lotus Sutra enjoins active missionary work in promulgating the Sutra and its teaching as follows: After entering the abode of the Tathagata, putting on his robe and sitting down on my seat, the preacher should, undaunted, expound this sutra. The strength of charity is my abode. The apparel of forbearance is my robe. And emptiness is my seat. Let the preacher take his stand on this and preach. Therefore, the principal message of the first half of the Lotus Sutra is: the Buddha`s skill in means, the doctrine of the One Vehicle, and the complete joy of the Buddha`s disciples in finding that they will, indeed they must, attain Perfect Buddhahood. The teaching of skill in means (or skilful means) is a crucial ancillary of one among the other principal doctrines of the Lotus Sutra, that of the One Vehicle (ekayana). The Buddha has employed his skill-in means and devices (upaya/upayakausalya) in order to adapt his teaching to the level of his hearers. The concept of skill in means extends to the core of Mahayana spirituality, and is one of the central teachings of the Lotus Sutra. Due to the issues around this concept, it has enabled the success of the Lotus Sutra in East Asian countries. Broadly speaking, the teaching of skill in means demonstrates the Buddha`s compassionate to adapt his teaching to the level of his hearers. The teaching, however, should be regarded as the ladders, or, to use an age-old Buddhist image, as a raft being employed to cross a river. There is no need to keep up with carrying the raft even though the journey has been already done. When used, such a teaching transcends itself. According to Nagarjuna in his Mulamadhyamakakarika XXIV, 18, it is dependent origination (pratityasamutpada) that we call the emptiness (sunyata). We might gloss this by saying that it is because entities originate in dependence on causes and conditions that they are empty. Here, emptiness is identified with the lack of inherent existence (nihsvabhava). In China, particularly in the Tien-t`ai tradition, the teaching of the Lotus Sutra was linked with that of the Mahaparinirvana Sutra, which advocates the tathagatagarbha doctrine, and also with that of the Awakening of Faith in Mahayana.