One time when the Buddha was dwelling at Sāvatthi*, a bhikkhu called Moḷiyaphagguno asked a series of related questions: Who consumes the nutriment of consciousness (ie receives the input from the senses)? Who makes contact? Who feels? Who craves? Who grasps? Sense impressions, sensations, craving, grasping are part of the list of nidānas or links - that is part of the sequence which is traditionally used to explain the workings of paṭiccasamuppāda or dependent arising. Each of the answers is similar and we can get a feel for the discourse by focussing on just one: craving.
‘‘Ko nu kho, bhante, tasatī’’ti? ‘‘No kallo pañho’’ti bhagavā avoca – ‘‘‘tasatī’ti ahaṃ na vadāmi. ‘Tasatī’ti cāhaṃ vadeyyaṃ, tatrassa kallo pañho – ‘ko nu kho, bhante, tasatī’ti? Evaṃ cāhaṃ na vadāmi. Evaṃ maṃ avadantaṃ yo evaṃ puccheyya – ‘kiṃpaccayā nu kho, bhante, taṇhā’ti, esa kallo pañho. Tatra kallaṃ veyyākaraṇaṃ – ‘vedanāpaccayā taṇhā, taṇhāpaccayā upādāna’’’nti. (SN 12:12; PTS S ii.13)Who craves, Sir? The Blessed One said "that is not a proper question". I don't say "he craves". If I did say "he craves", then it might be a proper question, but I don't talk like that. A proper question would be: "with what condition is there craving?" And the proper answer is that because of sensations, there is craving; and because of craving, there is grasping.
Note here that 'he craves' is tasati, while 'craving' (the verbal-noun) is taṇhā, this literally means 'thirst' and is a poetic metaphor for craving more generally. The relationship is more obvious in Sanskrit where the verb is tṛṣyati and the noun tṛṣṇā. Each of the verses is structured identically and identifies the condition and what is conditioned by it - that is the cause and the effect - of the element being asked about. Here the sequence is
vedanā > taṇha > upādānasensation > craving > graspingNote that the Buddha does not associate pronouns with the links. He does not speak in terms of "I crave", "you crave", "he/she/it craves". He talks in terms of "there is craving", and there is craving because the condition of sensation (vedanā) is present.** It is an application of the general principle "because of that being, this is (imasmiṃ sati, idam hoti)" to the existence of craving.

So the agent of craving is not a person, it is the process of paticcasamuppāda. Craving is in fact impersonal. Craving arises because there is sensation.*** By the way I have taken to translating vedanā as 'sensations' rather than the more usual 'feelings', because in English we talk about our emotions as 'feelings' and this is not what is intended in the Buddhist term. Emotions are a down stream product of experiencing vedanā that emerge as a result of papañca.

An interesting conclusion here is that we aren't personally responsible for the arising of craving (or hatred) in the present. There can be no doubt that we are responsible for our present actions, but because of the situation we are in, if there is sensation then there will automatically be craving - until we are awakened this is involuntary. But we don't need to feel guilty about experiences which have arisen in dependence on causes. The text is not trying to pin the blame on anyone. There can be no blame for a natural process. We don't blame rain for being wet. This exposes an aspect of the ancient Buddhist world view which is that some things are dhammatā - the natural thing, a natural law. Dhammatā literally means lawfulness - it is an abstract noun from dhamma in the sense of law or principle.

The Buddha is saying then that the arising of craving in dependence on sensations is a natural process, a natural law even. Such things as craving are unavoidable, they just happen. However we cannot rest here, because the rest of the story is that where there is craving there is grasping (upādāna), and grasping is the fuel (a more literal meaning of upādāna) for becoming (bhava) which leads to birth, old age, and death - in other words it all leads to dukkha, to sokaparidevadukkhadomanassupāyāsā - grief, lamenting, misery, dejection, and trouble. So if we simply acquiesce to this process then we are stuck with the misery of it.

Fortunately for us there are other dhammatā or natural laws (or other aspects of the law) which means we can address the problem of suffering in two basic ways. Firstly by removing the causes: where there is no craving there is no grasping, where there is no contact there is no craving, etc which is the solution recommended by this sutta. When this ceases, that ceases also. Secondly we can try to cultivate positive states. For instance through practising ethics, we generate non-remorse, which gives rise to joy, to rapture, etc, which we know after Sangharakshita as 'the spiral path'. There are a few variants on the spiral path in the canon (for a list see my essay A Footnote to Sangharakshita's A Survey of Buddhism). The spiral path also represents a dhammatā in that the texts say that if we only begin and persist, the effects will follow quite naturally. Both of these approaches lead to freedom from suffering - the ultimate goal of the Buddha's path in the Pāli texts.

A note here for Mahāyanists: it's often said that the so-called 'Arahant Ideal', the ideal of awakening propagated in the Pāli texts is selfish. It's clear from this text that the ideas of a self or the idea of my suffering or my awakening, are not properly phrased. The Buddha does not talk in terms of I, me, mine; thou, thy, thine; or he, him, his etc. There can be no question therefore of only practising to remove "my suffering", because "my suffering" is an improper use of language. It is simply that there is suffering, and it arises in dependence on a cause. One can either remove the cause, or one can cultivate the opposite, but "I" doesn't come into it. While compassion for all beings, or awakening for the sake of all beings is more explicit in Mahāyana discourse, it is only a restatement of something implicit in the Pāli texts, something which perhaps did not need to be stated so boldly at the time.

Once again this texts focuses on the nature of experience - sensory input and how we process it. It seems especially important to understand the nature of this relationship between sensations, craving, and grasping. It is equally important not to get caught up in trying to figure out what Reality is, or dwelling on metaphysics. You have access to all the information you need - it is your own experience. What is required is a systematic investigation of your experience of things, which does not require much in the way of definitions and discussion, or even education for that matter. If you can sit quietly and pay attention to the effects of sensations on mind/body, then you are well on your way.



Notes
* The Moḷiyaphagguna Sutta is in the Saṃyutta Nikāya (SN 12:12; PTS S ii.13). My translation based on the Pāli text from tipitika.org. Translated by Bhikkhu Bodhi on pg 541-2 in his Connected Discourses of the Buddha; and by Bhikkhu Thanissaro on Access to Insight as the Phagguna Sutta.
** It is a quirk of Pāli and Sanskrit that one doesn't need to use a verb "to be" in order to assert the existence of something. Just stating 'taṇhā' is sufficient. Although one can say 'taṇhā hoti' - there is suffering - in these Pāli sentences 'to be' is not used, but is understood. Note that this way of talking without pronouns is similar to some of the ways that Benjamin Lee Whorf records being used amongst indigenous Americans.
*** I think this view of dependent arising as impersonal and the eschewing of pronouns is an argument against a literal reading of rebirth, but that is a more complex story than I can address here.