The foundational pasuk is Bereishit 2:7, which describes God forming man from dust and blowing into his nostrils a breath of life, so that the human became a living being — the verse from which the entire tradition of soul-analysis flows.
Bereshit Rabbah 14:9 is the locus classicus for the five-part framework: it names the soul by five terms — nefesh, ruach, neshamah, chayah, yechidah — and assigns each a distinct function: nefesh is identified with the blood (citing Devarim 12:23), ruach is that which rises and descends, neshamah is the character or inner disposition (אופייא), chayah is what remains alive in the body when the other limbs die, and yechidah is singular in the body as no other organ is.
Nefesh HaChayim, Gate I 14:12 cites Bereshit Rabbah 14:9 directly and specifies that neshamah — whose primary seat is the brain — is the faculty of thought and intellect, the dimension that teaches a person knowledge and understanding of Torah.
Rabbeinu Bahya, Bereshit 2:7 documents a live machlokes among the philosophical authorities: one school holds that the soul is one entity with three powers — the appetitive (shared with animals), the vegetative (shared with plants), and the rational (distinctively human) — while a second school holds that these are three entirely separate souls, each with its own independent existence, with the animal soul seated in the liver and identified with both nefesh and ruach, driving appetite and anger.
Guide for the Perplexed, Part 1 41 takes yet a different approach, reading nefesh as a homonymous term covering at least five distinct meanings: the vitality common to all creatures, blood, the rational faculty that distinguishes man, the part that persists after death, and will — treating the soul not as a set of metaphysical levels but as a word requiring careful disambiguation.
Mishneh Torah, Foundations of the Torah 4:8-9 identifies the distinctively human soul with the intellectual form (tzurat ha-adam), which knows and apprehends non-material ideas in the manner of angels — distinguishing it sharply from the soul shared with all living flesh that animates eating and movement.
רמח"ל, כללי חכמת האמת maps the five levels onto the five divine partzufim of Kabbalah — nefesh from Nukvah, ruach from Ze'ir Anpin, neshamah from Imma, chayah from Abba, yechidah from Arikh Anpin — and adds that souls originating in each of the four worlds (Asiyah, Yetzirah, Beriah, Atzilut) bear corresponding names, with an additional dimension called the tzelem serving as a garment through which all these levels enter and stand within the body.
Derekh Hashem, Part Three, On the Soul and Its Activities:4 affirms that what is called 'one soul' in general terms is in truth composed of many levels and gradations, linked like the links of a chain, and that the full complement of soul-parts divides into the same five: nefesh, ruach, neshamah, chayah, yechidah — adding the observation that the additional soul that arrives on Shabbat and departs at its close belongs to this larger chain and its arrival and departure are not felt by the body.
זהר, זהר חדש בראשית רות שמט, ועיין שם עוד וערך נשמה teaches that God gave the human being two primary levels — nefesh and ruach — for service in this world: nefesh to sustain the body through the performance of mitzvot, and ruach to be aroused through Torah study and to guide a person in this world; and that only when both are employed faithfully does the higher gift of neshamah (and beyond it chayah and yechidah) descend upon the person from above.
Tanya, Part I; Likkutei Amarim 1:15 introduces a further structural distinction unique to its approach: every Jew possesses two souls — an animal soul rooted in the kelipah that enlivens the body through the blood, from which derive anger, pride, and other traits tied to the four negative elements, and a divine soul — and Tanya, Part I; Likkutei Amarim 9:1 locates these two souls anatomically: the animal soul resides in the left ventricle of the heart where the blood pools, while the divine soul is seated in the brain and extends to all limbs and also to the right ventricle of the heart where there is no blood.
Tanya, Part I; Likkutei Amarim 3:1 specifies that each of the three lower soul-levels — nefesh, ruach, and neshamah — is itself composed of ten dimensions corresponding to the ten supernal sefirot, divided into three intellectual faculties (chokhmah, binah, da'at) and seven emotive ones (chesed, gevurah, tiferet, and the rest), and Tanya, Part I; Likkutei Amarim 2:5 notes that despite infinite gradations of souls across generations, every individual soul comprises nefesh, ruach, and neshamah within itself.
Maamar HaChochmah, Chelek 1 13:1 explains that the five parts of the separated soul can each undergo gilgul independently — being reincarnated in a second or third body — and that typically not all parts require reincarnation, since those portions that were rectified during a lifetime need not return, while only the unrepaired portions do; and Maamar HaChochmah, Chelek 1 13:2 clarifies that the number of soul-portions a person carries does not increase or diminish his vitality or intellect, since vitality and thought depend on the rational soul (nefesh ha-medaberet) that each person possesses individually.
Nefesh HaChayim, Gate I 5:9 teaches that only the 'heel-portion' of the soul's root actually enters the body, while the essential part of the soul remains planted above, extending through myriads of worlds like a rope, so that all of a person's deeds stir the upper root — pulling the far end of the rope moves the near end as well.
Nefesh HaChayim, Gate I 6:3 adds the cosmological dimension: man was created last as an integrating power encompassing all the higher lights, worlds, and palaces that preceded him, so that every particular power within a person corresponds to a specific world or force in the upper and lower realms.
Asara Maamarot, Em Kol Chai 2:11 connects the five soul-names to the principle that God alone is their proximate cause, and finds a scriptural allusion to the parts of the human being — body, soul, and the intermediate forms — in the verse 'the singers went before, then the players; in the midst were the damsels playing timbrels' (Tehillim 68:26), with the praise rising from the soul being like song without instrument, that from the body like instrumental music, and the intermediate forms like the damsels in between.
Asara Maamarot, Olam Katan 2 distinguishes between nefesh, ruach, and neshamah — which require a garment (levush) in order to enter the body and which extend from the worlds of Beriah, Yetzirah, and Asiyah to every native Israelite and sincere convert — and chayah and yechidah, which are in the category of 'head' and require no such garment and bear no relation to the body in the same way.
Ibn Ezra on Tehillim 35:9 notes that the term nefesh in that verse alludes to the higher neshamah, the word nefesh being used because the neshamah is bound up with it — a brief but telling remark that the names overlap and cannot always be read in strict separation.
Kli Yakar on Bereishit 2:7 observes that despite receiving the rational neshamah at creation, man begins his existence as merely a generic nefesh chayah like other living creatures, and his perfection depends on his own diligence and choice — so that the verse pointedly omits the divine assessment 'and God saw that it was good' at the moment of man's formation, because at that moment his goodness was not yet apparent.
Ein Aya, Berakhot 6:68 reflects on the interplay of body and soul, noting that physical strengthening through food and regimen reinforces the soul's activity, while strengthening the vital spirit through appropriate soul-activities reinforces the body in turn — and identifies this as evidence of Chazal's clear view that the vital power in animals participates in the same soul-faculty as that of man.
Niddah 30b:21 provides the Gemara's teaching that the soul of a fetus is taught the entire Torah in the womb, and that upon birth an angel strikes the child on the mouth causing total forgetting — implying that the soul's highest capacity pre-exists the body and is only constrained by entering it.
Avot DeRabbi Natan 31b recounts the twelve-hour sequence of Adam's creation, marking the sixth hour as the moment a soul was infused — placing the bestowal of the soul as a distinct, dateable event within the formation of the human body.
Tanya, Part I; Likkutei Amarim 19:4 describes the soul's deepest natural longing: neshamah, ruach, and nefesh together desire by their very nature to separate from the body and cleave to their source and origin in God — even at the cost of their own annihilation of essence — and this is their inherent will.
Ein Aya, Berakhot 9:191 reflects that the human being is composed of two full systems — the faculty of feeling and imagination that produces poetry, and the rational faculty that produces judgment — and that each requires its own complete arena, so that the emotional power not be disturbed by the expansion of reason, nor reason impeded by emotion; Guide for the Perplexed, Part 2 36 likewise identifies the rational faculty and the imaginative faculty as the two channels through which the divine overflow of prophecy reaches man, with the imaginative faculty requiring the highest natural development.