hetu? prak?tir ucyate
puru?a? sukha-du?khana?
bhokt?tve hetur ucyate

Translation of Bhagavad Gita 13.21

Nature is said to be the cause of all material causes and effects, whereas the living entity is the cause of the various sufferings and enjoyments in this world.

Commentary by Sri A.C. Bhaktivedanta Swami Prabhupada of Gaudiya Sampradaya:

The different manifestations of body and senses among the living entities are due to material nature. There are 8,400,000 different species of life, and these varieties are creations of the material nature. They arise from the different sensual pleasures of the living entity, who thus desires to live in this body or that. When he is put into different bodies, he enjoys different kinds of happiness and distress. His material happiness and distress are due to his body, and not to himself as he is. In his original state there is no doubt of enjoyment; therefore that is his real state. Because of the desire to lord it over material nature, he is in the material world. In the spiritual world there is no such thing. The spiritual world is pure, but in the material world everyone is struggling hard to acquire different kinds of pleasures for the body. It might be more clear to state that this body is the effect of the senses. The senses are instruments for gratifying desire. Now, the sum total—body and instrument senses—are offered by material nature, and as will be clear in the next verse, the living entity is blessed or damned with circumstances according to his past desire and activity. According to one’s desires and activities, material nature places one in various residential quarters. The being himself is the cause of his attaining such residential quarters and his attendant enjoyment or suffering. Once placed in some particular kind of body, he comes under the control of nature because the body, being matter, acts according to the laws of nature. At that time, the living entity has no power to change that law. Suppose an entity is put into the body of a dog. As soon as he is put into the body of a dog, he must act like a dog. He cannot act otherwise. And if the living entity is put into the body of a hog, then he is forced to eat stool and act like a hog. Similarly, if the living entity is put into the body of a demigod, he must act according to his body. This is the law of nature. But in all circumstances, the Supersoul is with the individual soul. That is explained in the Vedas (Mundaka Upanishad 3.1.1) as follows: dva suparna sayuja sakhayah. The Supreme Lord is so kind upon the living entity that He always accompanies the individual soul and in all circumstances is present as the Supersoul, or Paramatma.

Commentary by Sri Vishvanatha Chakravarthi Thakur of Gaudiya Sampradaya:

In this verse the Lord shows the jiva’s connection with prakrti. Prakrti is the cause of the jiva’s unfortunate condition by his misidentification with the body (karya), the senses which produce happiness and distress (karana) and the presiding deities of the senses (kartr). Prakrti, by association with the jiva, transforms into the form of body, senses and sense devatas, and, by its function of ignorance, it becomes the bestower of the jiva’s misidentification.

The jiva (purusa), having the position as the enjoyer of the happiness and distress produced by prakrti, is also the cause of the connection.

The meaning is this. Even though the body, the senses, the sense devatas and the jiva’s capacity for enjoyment (bhoktrtva) are all qualities of prakrti, because of the predominance of unconsciousness in the body, senses and sense devatas, and the predominance of consciousness in experiencing happiness and distress (bhoktr), the two get separately designated as causes according to predominance. According to this reasoning, it is said that prakrti is the cause, by producing the body, sense and sense devatas, and jiva is the cause by his capacity to experience happiness and distress.

Commentary by Sri Ramanuja of Sri Sampradaya:

13.21 The ‘Karya’ means the body, the ‘Karanas’ mean the instruments, i.e., the senses of perception and action plus the Manas. In their operations, the Prakrti, subservient to the self, is alone the causal factor. The sense is that their operations, which are the means of experience, have their foundation in the Prakrti, which has developed in the form of the body subservient to the self. In regard to this, the authority is the aphorism, ‘The self is an agent, on account of the scriptures having the purpose’ (B. S., 2.3.33) etc. The agency of the self means that the self is the cause of the will (effort) to support the body. The self (Purusa) associated with the body is the cause for experiencing pleasures and pains. The meaning is that It is the seat of those experiences. Thus, has been explained the difference in the operations of the Prakrti and of the self when they are mutually conjoined. He now proceeds to explain how, though the self, which in Its pristine nature experiences Itself by Itself as nothing but joy, becomes the cause of experiencing both pleasure and pain derived from sense objects when It is conjoined with a body. The term Guna figuratively represents effects. The self (in Its pristine nature) experiences Itself by Itself, as nothing buy joy. But when dwelling in the body, i.e., when It is in conjunction with the Prakrti, It experiences the qualities born of Prakrti, namely, happiness, pain etc., which are the effects of Gunas like Sattva etc. He explains the cause of conjunction with the Prakrti:

Commentary by Sri Sridhara Swami of Rudra Sampradaya:

After explaining how the evolution of all jivas or embodied beings along with their modifications and transformations all arise from prakriti or the material substratum pervading physical existence, Lord Krishna elaborates how the Purusa or eternal manifestation of the Supreme Lord as the atma or immortal soul is hetuh or responsible for determining one’s transmigratory existence. The effect of this is the physical body, the cause is the means to experience the dualities such as joy and distress if the senses and their production is from the gunas or the actions of goodness, passion and ignorance producing karma or reactions from past actions making the subsequent modifications and transformations. Prakriti is the cause of the position of the physical body as confirmed by Kapila and Vedavyasa. The Purusa manifested as the atma is the cause of the happiness and misery experienced which are of its own making. Although the inert prakriti cannot by itself be considered the cause it is the source of the physical mnaifestation. Neither can the Purusa which is immortal and changeless experience anything; but inexplicably it happens to both and by agency of its auspices it is accomplished. The agency referred to here is that of adrishta or the cumulative results of karma which acts as a sentient principle upon even the insentient. The same as fire burns upwards, rivers flow downwards, the wind blows obliquely and milk from the cow spurts outwards. Therefore this agency of the insentient prakriti is said to be due to the influence of the Purusa by the experience of cognition in both joy and misery, happiness and distress and all such dualities. Whereas these being the qualities of only sentient beings the experience of the Purusa is said to be due to the proximity of prakriti.

Commentary by Sri Madhvacharya of Brahma Sampradaya:

The word karyam meaning effect verily signifies the physical body. The word karana meaning cause reinforces the reality that the physical body is the instrument of performing actions. The word bhoktrtve means experiencing. Lord Krishna as the purusa a manifestation of the Supreme Lord as unlimited consciousness is the cause witnessing and experiencing through all jivas or embodied beings. Prakriti or the material substratum pervading material existence is the effect of actions and the purusa being superior is the cause of action.

Now begins the summation.

It is prakriti in the form of maya or the external illusory energy that bewilders jivas into believing the physical body belongs to them and is acquired on ones own independently; due to being completely oblivious of the reality of Lord Krishna as the sole creator of everything in all times throughout all creation and it is He alone who awards the power of the jivas to experience the ksetra or field of activity within the physical body and within material existence. Lord Krishna is known as the Supreme Controller because everything in exsitence emanates originally from Him in the material worlds and Vaikuntha the spiritual worlds. Even though the Supreme Lord creates everything, to show that the privilege of experience has been granted to prakriti to a small degree, He uses the word ucyate or speaks in two places. The puport is to emphasize the purusa is the principle cause and prakriti is the secondary effect. Specifically prakriti is more an instrument of action then experiencing actions. The jiva to a lesser extent has been granted agency for experiencing and enjoyment but the actual experiencer and enjoyer is the Supreme Lord who is the controller of everything and who is known as the purusa and ordains through the medium of His localized aspect of paramatma the supreme soul present in the etheric heart of all living entities.

Commentary by Sri Keshava Kashmiri of Kumara Sampradaya:
Lord Krishna having explained the evolutionary cycle of material nature, He explains of the respective functions of matter and spirit as they exist conjointly. The words karya-karana-kartrtve mean the results of the combination of the evolution of the bodily organs and functions and the influence of the presiding demigods on the senses which when coming in contact with matter are the cause of the jiva or embodied soul to be in bondage experiencing the consequence of their karma or reactions to good and bad actions and obliged to accept happiness and misery. This is unavoidable as long as one remains infatuated and attracted to material existence.

Commentary by Sri Adi Shankaracharya of Advaita Sampradaya:

13.21 Karya-karana-kartrtve, with regard to the source of body and organs: Karya is the body, and karana are the thirteen [Five sense organs, five motor organs, mind, intellect and ego.] organs existing in it. Here, by the word karya are understood the aforesaid elements that produce the body as also the objects which are modifications born of Nature. And since the qualities-which are born of Nature and manifest themselves as happiness, sorrow and delusion-are dependent on the organs, (therefore) they are implied by the word karana, organs. The kartrtvam, (lit) agentship, with regard to these body and organs consists in being the source of the body and organs. With regard to this source of the body and organs, prakrtih, Nature; ucyate, is said to be; the hetuh, cause, in the sense of being the originator. Thus, by virtue of being the source of body and organs, Nature is the cause of mundane existence. Even if the reading be karya-karana-kartrtva, karya (effect, modification) will mean anything that is the transformation of something; and karana (cause) will be that which becomes transformed. So the meaning of the compund will be: ‘with regard to the source of the effect and the cause’. Or, karya means the sixteen [The eleven organs (five sensory, five motor, and mind) and the five objects (sound etc.).] modificaitons, and karana means the seven [Mahat, egoism, and the five subtle elements.] transformations of Nature. They themselves are called effect and cuase. So far as the agentship with regard to these is concerned Nature is said to be the cause, because of the same reason of being their originator. As to how the soul can be the cause of mundane existence is being stated: Purusah, the soul, the empirical being, the knower of the field-all these are synonymous; is the hetuh, cause; bhoktrtve, so far as enjoyership, the fact of being the perceiver; sukha-duhkhanam, of happiness and sorrow-which are objects of experience, is concerned. How, again, is it asserted with respect to Nature and soul that, they are the causes of mundane existence by virtue of this fact of their (respectively) being the source of body and organs, and the perceiver of happiness and sorrow? As to this the answer is being stated: How can there be any mundane existence if there be no modification of Nature in the form of body and organs, happiness and sorrow, and cause and effect, and there be no soul, the conscious being, to experience them? On the other hand, there can be mundane existence when there is a contact, in the form of ignorance, between Nature-modified in the form of body and organs, and cause and effect as an object of experience and the soul opposed to it as the experiencer. Therefore it was reasonable to have said that, Nature and soul become the cause of mundane existence by (respectively) becoming the originators of the body and organs, and the perceiver of happiness and sorrow. What again is this that is called worldly existence? Worldly existence consists in the experience of happiness and sorrow; and the state of mundane existence of the soul consists in its being the experiencer of happiness and sorrow. It has been asserted that the state of mundane existence of the soul consists in its being the experiencer of happiness and sorrow. How does it come about? This is being answered:

Commentary by Sri Abhinavagupta of Kaula Tantra Sampradaya:

13.20-23 Prakrtim etc. upto parah. The Material Cause also is beginningless, because it has no other casue. Modifications : the cloth and the like. What is known as Material Cause is the basis for the process of cause-and-effect. But, the Soul, because of Its importance, constitutes the enjoyer. [Thus] the Material Cause and the Soul have verily an existence of interdependence just as that of the lame and the blind. Hence, the nature of the Soul is described by the authors of the scriptures by nomenclatures having different forms such as ‘the Spectator’ and so on. The meaning, intended here is this : The Material Cause, Its modifications, the fourteen types of creation and also the Soul – this is all beginningless and perennial as it is completely illuminated by the category Brahman and is identical with it. Hence [the Bhagavat] said :

Sanskrit Shloka Without Transliteration Marks:

hetuh prakrtir ucyate
purusah sukha-duhkhanam
bhoktrtve hetur ucyate

Sanskrit to English Word for Word Meanings:

karya — of effect; kara?a — and cause; kart?tve — in the matter of creation; hetu? — the instrument; prak?ti? — material nature; ucyate — is said to be; puru?a? — the living entity; sukha — of happiness; du?khanam — and distress; bhokt?tve — in enjoyment; hetu? — the instrument; ucyate — is said to be.