Grammar Analysis: Hebrews 1:8-10¶

Text¶

Greek (Nestle 1904):

v.8 πρὸς δὲ τὸν Υἱόν Ὁ θρόνος σου ὁ Θεὸς εἰς τὸν αἰῶνα τοῦ αἰῶνος, καὶ ἡ ῥάβδος τῆς εὐθύτητος ῥάβδος τῆς βασιλείας αὐτοῦ.
v.9 ἠγάπησας δικαιοσύνην καὶ ἐμίσησας ἀνομίαν· διὰ τοῦτο ἔχρισέν σε, ὁ Θεός, ὁ Θεός σου ἔλαιον ἀγαλλιάσεως παρὰ τοὺς μετόχους σου.
v.10 καί Σὺ κατ᾽ ἀρχάς, Κύριε, τὴν γῆν ἐθεμελίωσας, καὶ ἔργα τῶν χειρῶν σού εἰσιν οἱ οὐρανοί·

KJV:

v.8 But unto the Son [he saith], Thy throne, O God, [is] for ever and ever: a sceptre of righteousness [is] the sceptre of thy kingdom.
v.9 Thou hast loved righteousness, and hated iniquity; therefore God, [even] thy God, hath anointed thee with the oil of gladness above thy fellows.
v.10 And, Thou, Lord, in the beginning hast laid the foundation of the earth; and the heavens are the works of thine hands.

OT Source Texts (KJV):

Psalm 45:6 Thy throne, O God, [is] for ever and ever: the sceptre of thy kingdom [is] a right sceptre.
Psalm 45:7 Thou lovest righteousness, and hatest wickedness: therefore God, thy God, hath anointed thee with the oil of gladness above thy fellows.
Psalm 102:25 Of old hast thou laid the foundation of the earth: and the heavens [are] the work of thy hands.
Psalm 102:26-27 They shall perish, but thou shalt endure... But thou [art] the same, and thy years shall have no end.

Word-by-Word Parsing¶

Hebrews 1:8¶

#	Word	Lemma	Strong	Parsing
1	πρὸς	πρός	G4314	PREP
2	δὲ	δέ	G1161	CONJ
3	τὸν	ὁ	G3588	T-ASM
4	Υἱόν	υἱός	G5207	N-ASM
5	Ὁ	ὁ	G3588	T-NSM (nominative-form article)
6	θρόνος	θρόνος	G2362	N-NSM "throne"
7	σου	σύ	G4771	P-2GS "thy"
8	ὁ	ὁ	G3588	T-NSM
9	Θεὸς	θεός	G2316	N-NSM "God"
10	εἰς	εἰς	G1519	PREP
11	τὸν	ὁ	G3588	T-ASM
12	αἰῶνα	αἰών	G165	N-ASM
13	τοῦ	ὁ	G3588	T-GSM
14	αἰῶνος	αἰών	G165	N-GSM
15	καὶ	καί	G2532	CONJ
16	ἡ	ὁ	G3588	T-NSF
17	ῥάβδος	ῥάβδος	G4464	N-NSF "sceptre"
18	τῆς	ὁ	G3588	T-GSF
19	εὐθύτητος	εὐθύτης	G2118	N-GSF "uprightness"
20	ῥάβδος	ῥάβδος	G4464	N-NSF
21	τῆς	ὁ	G3588	T-GSF
22	βασιλείας	βασιλεία	G932	N-GSF
23	αὐτοῦ	αὐτός	G846	P-GSM "his"

Hebrews 1:9¶

#	Word	Lemma	Strong	Parsing
1	ἠγάπησας	ἀγαπάω	G25	V-AAI-2S "thou lovedst"
2	δικαιοσύνην	δικαιοσύνη	G1343	N-ASF "righteousness"
3	καὶ	καί	G2532	CONJ
4	ἐμίσησας	μισέω	G3404	V-AAI-2S "thou hatedst"
5	ἀνομίαν	ἀνομία	G458	N-ASF "lawlessness"
6	διὰ	διά	G1223	PREP
7	τοῦτο	οὗτος	G3778	D-ASN
8	ἔχρισέν	χρίω	G5548	V-AAI-3S "he anointed"
9	σε	σύ	G4771	P-2AS
10	ὁ	ὁ	G3588	T-NSM
11	Θεός	θεός	G2316	N-NSM (first ὁ Θεός)
12	ὁ	ὁ	G3588	T-NSM
13	Θεός	θεός	G2316	N-NSM (second ὁ Θεός σου)
14	σου	σύ	G4771	P-2GS
15	ἔλαιον	ἔλαιον	G1637	N-ASN "oil"
16	ἀγαλλιάσεως	ἀγαλλίασις	G20	N-GSF "of gladness"
17	παρὰ	παρά	G3844	PREP ("above, beyond")
18	τοὺς	ὁ	G3588	T-APM
19	μετόχους	μέτοχος	G3353	A-APM "fellows/partakers"
20	σου	σύ	G4771	P-2GS

Hebrews 1:10¶

#	Word	Lemma	Strong	Parsing
1	καί	καί	G2532	CONJ
2	Σὺ	σύ	G4771	P-2NS emphatic "thou"
3	κατ᾽	κατά	G2596	PREP
4	ἀρχάς	ἀρχή	G746	N-APF "beginnings"
5	Κύριε	κύριος	G2962	N-VSM (true morphological vocative!)
6	τὴν	ὁ	G3588	T-ASF
7	γῆν	γῆ	G1093	N-ASF "earth"
8	ἐθεμελίωσας	θεμελιόω	G2311	V-AAI-2S "thou foundedst"
9	καὶ	καί	G2532	CONJ
10	ἔργα	ἔργον	G2041	N-NPN "works"
11	τῶν	ὁ	G3588	T-GPF
12	χειρῶν	χείρ	G5495	N-GPF "of hands"
13	σού	σύ	G4771	P-2GS
14	εἰσιν	εἰμί	G1510	V-PAI-3P "are"
15	οἱ	ὁ	G3588	T-NPM
16	οὐρανοί	οὐρανός	G3772	N-NPM "heavens"

Key Grammatical Features¶

1. ὁ Θεός (Heb 1:8) — Nominative-Form Article + Noun Addressed to the Son¶

Form: Both ὁ and Θεός are parsed N-NSM / T-NSM (nominative singular masculine). Morphologically, this is the nominative form, not the distinct vocative form (which for θεός would be θεέ, a genuine morphological vocative that occurs in Matt 27:46 θεέ μου).
The interpretive question: How should Ὁ θρόνος σου ὁ Θεὸς εἰς τὸν αἰῶνα τοῦ αἰῶνος be construed? Three readings are grammatically permitted:
Vocative of address ("Thy throne, O God, is for ever and ever"): Greek regularly uses the articular nominative as a form of address (= "nominative for vocative"), especially when reproducing Hebrew vocative-with-article. KJV, ESV, NIV, NASB, NRSV, CSB all translate this way. The LXX of Psa 45:7 (LXX 44:7) reads identically, and it renders MT אֱלֹהִים — a vocative form in its Hebrew context (vocative-noun with no preceding preposition or verb governing it).
Nominative of predication ("God is your throne for ever and ever"): Treats ὁ Θεός as subject and ὁ θρόνος σου as predicate, or vice versa — "Your throne is God…" or "God is your throne…". This reading is grammatically possible because Greek copular clauses permit either constituent as subject, but (a) it produces a strained sense, (b) it ignores the parallelism with v.10 where the Son is directly addressed as Κύριε (true vocative), and (c) it breaks the fourfold σου-address chain that the Hebrews author's quotation preserves.
Nominative as verbless descriptive ("Your throne-of-God is for ever"): Treats ὁ Θεός as some kind of genitive-equivalent modifying θρόνος. Morphologically this is ruled out — Θεός is nominative, not genitive (which would be Θεοῦ). Found only in non-standard reconstructions.
Why reading #1 is preferred by the Hebrews author's own syntax:
Parallelism with v.10: v.10 directly addresses the Son as Κύριε — a true morphological vocative (κύριος → κύριε), leaving no doubt that the Father is addressing the Son by divine titles. The vocative of v.10 retrospectively licenses the vocative reading of v.8.
The σου-chain: vv.8-12 contain ten 2nd-person pronouns addressed to the Son (σου, σε, σοῦ, σύ, σού) — v.8 sits inside a consistent direct-address frame.
The contrast with v.9b: v.9 contains a clearer nominative-of-predication use (ὁ Θεός, ὁ Θεός σου = "God, even thy God") where the two nominative phrases together function as the explicit subject of ἔχρισέν. v.9's second ὁ Θεός is unambiguously subject-of-verb nominative; v.8's ὁ Θεός has no verb it can be subject of (the clause is verbless copular). This grammatical asymmetry between v.8 and v.9 is itself the argument that v.8's ὁ Θεός is not functioning as subject.
LXX Psa 44:7 (Hebrew 45:6) MT vocative: MT reads כִּסְאֲךָ אֱלֹהִים עוֹלָם וָעֶד. Hebrew אֱלֹהִים here is grammatically unbound vocative (no preposition, no verb taking it as argument, no construct-chain binding — it freely addresses the king). LXX-translators reproduce this with articular nominative (standard LXX habit for Hebrew vocative, since Greek has no article-article-vocative combined form). The Hebrews author takes this over verbatim.
Morphological note on the absence of θεέ: Greek θεός has both a formal vocative θεέ (rare, Matt 27:46) and an articular-nominative-as-address form ὁ θεός (common). The author's retention of LXX ὁ θεός (against any stylistic "correction" to θεέ) reflects Septuagintal vocative convention, not avoidance of direct address. Vocative-force is signalled by the article + proper-designation + context of address, not by morphological vocative ending. See greek/case-vocative-articular-nominative-address (not yet created — flagged gap).
Grammar reference: gap flagged — create greek/case-vocative-articular-nominative-address and greek/nominative-for-vocative.
Word study: G2316-theos, G2362-thronos, WG-throne.

2. εἰς τὸν αἰῶνα τοῦ αἰῶνος (Heb 1:8) — Emphatic Eternity Formula¶

Form: Prepositional phrase εἰς + accusative αἰῶνα + articular genitive τοῦ αἰῶνος (superlative-intensifying genitive chain, "unto the age of the age").
Significance: LXX Psa 44:7 identical. This is the strongest single-clause eternity formula in the NT beyond εἰς τοὺς αἰῶνας τῶν αἰώνων (plural-doubled, Rev 1:6 et al.). Its placement as predicate of the throne directly addressed to ὁ Θεός reinforces that the Son's reign is predicated in the same terms that the Psalter applies to YHWH's kingship (Psa 10:16; 29:10; 146:10).
Grammar reference: gap flagged — greek/idiom-eis-ton-aiona-tou-aionos.

3. ἠγάπησας / ἐμίσησας / ἔχρισέν (Heb 1:9) — Triple Aorist Active Indicative Sequence¶

Form: Three aorist active indicatives. First two are 2nd singular (ἠγάπησας, ἐμίσησας) addressed to the Son. Third is 3rd singular (ἔχρισέν) with ὁ Θεός as its subject and σε as object — "God anointed thee."
Significance: The grammatical person-switch is the crux. Verses 8-9a address the Son in 2nd person ("thy throne… thou hast loved…"). V.9b breaks to 3rd person with ὁ Θεός as agent of anointing directed at the Son. This produces the grammatical paradox the Hebrews author exploits: the Son is addressed as Θεός in v.8, and then at v.9b a distinct ὁ Θεός acts upon him ("God, thy God, anointed thee"). The nominative doubled phrase ὁ Θεός, ὁ Θεός σου reproduces MT Psa 45:8 אֱלֹהִים אֱלֹהֶיךָ ("God, thy God") — inner-Trinitarian address in which the speaker (Father) calls the addressee (Son) "God" and simultaneously identifies himself (Father) as the Son's "God." The Son has a God; the Son is addressed as God. Both are grammatically unambiguous from the morphology alone.
Parsing verified: hebrew_parser semantic of LXX Psa 44:8 ὁ Θεός, ὁ Θεός σου = MT 45:8 אֱלֹהִים אֱלֹהֶיךָ vocative-appositional pair.

4. Κύριε (Heb 1:10) — True Morphological Vocative¶

Form: κύριος → κύριε. This is a distinct morphological vocative singular masculine (N-VSM in parser output), NOT a nominative-for-vocative.
Significance: This is the decisive grammatical anchor for the identity of the addressee in the whole chain of quotations. In Psa 102 MT (Hebrew 102:1-28; English same) the Psalmist addresses YHWH (v.1 יְהוָה שִׁמְעָה תְפִלָּתִי; v.12 וְאַתָּה יְהוָה לְעוֹלָם תֵּשֵׁב; v.25 MT לְפָנִים הָאָרֶץ יָסַדְתָּ — "of old thou didst found the earth"). LXX Psa 101:26 supplies the explicit vocative σὺ, Κύριε, τὴν γῆν ἐθεμελίωσας, turning the subject-pronoun אַתָּה (MT implicit in the 2nd-singular verbal morphology) into the vocative-flagged Κύριε. The Hebrews author reproduces LXX verbatim.
The grammatical fact that drives the argument: in Psa 102 the LXX has already supplied Κύριε as vocative flag, and that Κύριε in LXX renders YHWH (the Tetragrammaton) of MT — not a generic ʾadonay or ʾadon. LXX Psa 101:1 title αὐτός + v.12 κύριε… + v.26 Κύριε all translate MT יְהוָה at the same verse positions. Therefore when the Hebrews author quotes Psa 102:25-27 at Heb 1:10-12 and applies σὺ… Κύριε to the Son, he is applying a text originally addressed to YHWH, with YHWH's divine name rendered as κύριος, directly to the Son in 2nd-person address — with a morphological vocative that rules out any "nominative-misreading" escape.
The argument structure is Septuagint-dependent: the Hebrews author's argument at v.10 presupposes LXX Κύριε = MT יְהוָה. A purely MT-based reading (where the vocative is not explicit but implicit in 2ms verbal morphology) retains the same force — the addressee of Psa 102:25 MT is unambiguously YHWH in context (vv.12, 15, 16, 19, 21, 22 all name YHWH as referent) — but the LXX's explicit vocative Κύριε makes the quotation self-contained and portable into the Hebrews argument without requiring reconstruction.
Word study: G2962-kyrios (check).
Grammar reference: gap flagged — greek/case-vocative-true-morphological (contrastable with articular-nominative-as-address above).

5. ἐθεμελίωσας (Heb 1:10) — Aorist Active Indicative 2ms of Creation¶

Form: V-AAI-2S of θεμελιόω G2311 ("to found, lay a foundation"). LXX Psa 101:26 supplies this for MT יָסַדְתָּ (Qal.Perf.2ms of יסד, "thou didst found").
Significance: The verb is 2nd person singular addressed to the Son (κύριε + σὺ in apposition). Its object is τὴν γῆν — the earth. This directly predicates creation of the material cosmos to the Son, using an OT text that addresses YHWH as creator. The following clause, ἔργα τῶν χειρῶν σού εἰσιν οἱ οὐρανοί ("the heavens are the works of thy hands"), predicates creation of the heavens to the same addressee via the 2ms possessive pronoun σού on χειρῶν. Paired with the v.12 σὺ δὲ ὁ αὐτὸς εἶ καὶ τὰ ἔτη σου οὐκ ἐκλείψουσιν ("thou art the same, and thy years shall not fail") this constitutes a grammatically complete divine-predication set: eternal pre-existence + creation-agency + immutability — every attribute the Psalm originally asserted of YHWH, now asserted of the Son by grammatical retention of the 2nd-person pronominal chain.

The Seven-Quotation Chain in Hebrews 1:5-13¶

The author of Hebrews assembles a chain of seven OT quotations in 1:5-13 to prove the Son's superiority over angels. The rhetorical structure pairs "to which of the angels did he say…" (τίνι / τίνα τῶν ἀγγέλων, vv.5, 13) as a frame, with five central quotations sandwiched inside:

#	Heb Ref	OT Source	Original Addressee	Applied to	LXX Vocative / Address Marker
1	1:5a	Psa 2:7	the Davidic king ("thou art my Son, this day have I begotten thee")	the Son	σύ (P-2NS) + σε (P-2AS), 2nd-person address; aorist γεγέννηκά σε
2	1:5b	2 Sam 7:14	Solomon / Davidic heir ("I will be to him a Father, and he shall be to me a Son")	the Son	3rd-person αὐτῷ / αὐτός, but royal-messianic promise read Christologically
3	1:6	Deut 32:43 LXX / Psa 97:7 LXX ("let all the angels of God worship him")	YHWH (MT Psa 97:7 reads אֱלֹהִים; Deut 32:43 LXX "all sons of God")	the Son	προσκυνησάτωσαν αὐτῷ — the referent "him" = YHWH in the original, applied to the Son at his enthronement
4	1:7	Psa 104:4	description of YHWH's action ("who maketh his angels winds")	angels (foil, demonstrating their creaturely/ministerial status)	3rd-person ὁ ποιῶν…
5	1:8-9	Psa 45:6-7	the Davidic king (royal wedding psalm; MT אֱלֹהִים addresses the king)	the Son	ὁ Θεός (articular-nom-as-address, v.8); explicit verbal direct-address throughout
6	1:10-12	Psa 102:25-27	YHWH (MT vv.1, 12, 15, 19, 21, 22 directly name יְהוָה; v.25 יָסַדְתָּ addresses YHWH)	the Son	Κύριε (true morphological vocative, v.10); σὺ emphatic
7	1:13	Psa 110:1 ("sit on my right hand until I make thine enemies thy footstool")	David's "Lord" (the messianic figure distinct from David himself)	the Son	κάθου (V-PNM-2S imperative to the Son); σου possessive

Pattern of the seven quotations as a theological argument built on grammatical facts:

Quotations 1 and 2 (Psa 2:7, 2 Sam 7:14) establish the Son as Davidic-messianic addressee — the "Son" vocabulary.
Quotation 3 (Deut 32:43 / Psa 97:7) makes the first quiet divine-identity move: angels worship him where the OT text originally worshipped YHWH. The Hebrews author has already begun transposing YHWH-references onto the Son.
Quotation 4 (Psa 104:4) is the foil: angels are described as creaturely agents of YHWH's will.
Quotations 5 and 6 are the double-climax and the exegetical hinge: Psa 45:6-7 addresses the Davidic king as אֱלֹהִים / ὁ Θεός, and Psa 102:25-27 addresses YHWH as the creator of earth and heavens. The Hebrews author applies both quotations to the same Son. Psa 45 already gave him a text where a human figure (Davidic king) is titled "God" — providing the precedent. Psa 102 then supplies the YHWH-passage that the Son must occupy if "God" in Psa 45 is to be anything stronger than honorific.
Quotation 7 (Psa 110:1) closes the chain with enthronement at the right hand — the session-formula that Hebrews will later develop in 8:1, 10:12, 12:2.

The grammatical move that makes Psa 102 applicable to the Son:

Psa 102:25-27 MT is uncontroversially addressed to YHWH (context of vv.1, 12, 15, 19, 21, 22 all name יְהוָה).
LXX Psa 101:26 renders the implicit MT vocative (MT: 2ms verb + 2ms pronoun addressed to already-named YHWH) with explicit Κύριε, the standard LXX rendering of the Tetragrammaton in vocative position.
The Hebrews author quotes LXX verbatim, keeping the Κύριε vocative intact.
His introductory formula (v.10 καὶ — "and…") continues πρὸς…τὸν Υἱόν from v.8b ("but unto the Son he saith"). The verb of saying (λέγει implicit from v.7, εἶπεν from v.5 — Hebrews' "God says X to the Son" formula runs through the whole chain) governs the whole series of quotations; it is the Father's address to the Son that runs from v.8 through v.12 uninterrupted.
Therefore the grammatical chain is: Father speaks → to the Son → using text from Psa 102 → which in its LXX source addresses YHWH-in-vocative-form-Κύριε.
The grammar does not permit reading the Κύριε of Heb 1:10 as anyone other than the Son, because (a) the introductory πρός + Son governs the whole extended quotation, (b) no new introductory formula intervenes between v.8 and v.13 (each is chained by καί), and (c) v.13's πρὸς τίνα δὲ τῶν ἀγγέλων εἴρηκέν ποτε closes the πρός-τὸν-Υἱόν address frame by contrastive reopening of the angels-question — which would be unintelligible unless everything from v.8 onward had in fact been spoken πρὸς τὸν Υἱόν.

This is the grammatical argument the Hebrews author makes: not a philological proof that Psa 102 "really means" the Son, but a transference authorized by the prior establishment of the Son as the addressee of the Father's divine-title speech (v.8 ὁ Θεός), such that a text originally addressed to YHWH can be reapplied to the Son without doing violence to the original referent — because the Son shares the identity being addressed. The grammatical form (Κύριε vocative, σύ emphatic, ἐθεμελίωσας 2ms creation-verb) survives the transposition intact; only the referent-resolution shifts, and that shift is licensed by the v.8 title.

Clause Structure Notes¶

v.8 — Three verbless/copular clauses addressed to the Son:¶

Ὁ θρόνος σου [ἐστίν] εἰς τὸν αἰῶνα τοῦ αἰῶνος — with ὁ Θεός as parenthetic vocative.
ἡ ῥάβδος τῆς εὐθύτητος [ἐστίν] ῥάβδος τῆς βασιλείας αὐτοῦ — note the person-shift from 2ms σου ("thy throne") to 3ms αὐτοῦ ("his kingdom") inside the same verse. The LXX/MT underlying Psa 45:7 (MT: שֵׁבֶט מַלְכוּתֶךָ "the sceptre of thy kingdom" — 2ms throughout) has been rendered in LXX with αὐτοῦ (3ms) for the last pronoun. This is a textual-critical crux — some Hebrews manuscripts read σου harmonizing to MT, others retain αὐτοῦ. It does not affect the Christological argument because the 2ms addressee is established by the preceding σου and the following v.9 ἠγάπησας.

v.9 — Three coordinate aorist-indicative clauses:¶

ἠγάπησας δικαιοσύνην (2ms aor.act.)
[καὶ] ἐμίσησας ἀνομίαν (2ms aor.act.)
διὰ τοῦτο ἔχρισέν σε, ὁ Θεός, ὁ Θεός σου, ἔλαιον ἀγαλλιάσεως… (3ms aor.act. with explicit nominative subject ὁ Θεός, ὁ Θεός σου; σε accusative of person; ἔλαιον ἀγαλλιάσεως double-accusative of thing anointed with — though some parse it as accusative of means with verbless-equivalent function)

v.10 — One aor.act. + one present-copular clause:¶

Σὺ κατ᾽ ἀρχάς, Κύριε, τὴν γῆν ἐθεμελίωσας (emphatic σύ + vocative Κύριε + 2ms aor.act.)
ἔργα τῶν χειρῶν σού εἰσιν οἱ οὐρανοί (3pl pres.act. εἰσίν with predicate-noun ἔργα preceding subject οἱ οὐρανοί in marked fronted-position — though subject/predicate directionality in Greek copular clauses with article-article pattern has known ambiguities per Wallace 42-46)

Cross-References¶

Grammar Library¶

Gap flagged: greek/case-vocative-articular-nominative-address — "nominative-for-vocative" convention (articular nominative used as direct address, especially in LXX renderings of Hebrew vocative)
Gap flagged: greek/case-vocative-true-morphological — true vocative forms (θεέ, κύριε, πάτερ) vs. articular-nominative address
Gap flagged: greek/idiom-eis-ton-aiona-tou-aionos — emphatic eternity formula
Gap flagged: greek/person-shift-lxx-quotation — person/pronoun discrepancies between LXX quotations and MT originals as they appear in NT citations
Related existing entry: greek/divine-passive (agent-suppression in v.9's ἔχρισέν is NOT divine-passive — subject is explicit ὁ Θεός)
Related existing entry: greek/son-of-X-semitic-idiom (for υἱός-titular language of Heb 1:5 and the context frame)

Word Studies¶

G2316-theos — θεός G2316
G2362-thronos — θρόνος G2362
WG-throne — throne English-reverse-lookup
Gap flagged: G2962-kyrios, G5207-huios, G25-agapao, G3404-miseo, G5548-chrio, G2311-themelioo, G746-arche, G1343-dikaiosune, G458-anomia, G3353-metochos

Passage Analyses¶

Companion entry: heb-6-13-18 (Hebrews author's use of OT oath-formulas)

OT Source-Text Passages (gaps flagged)¶

psa-45-6-7 (Hebrew grammar of MT Psa 45:7 vocative אֱלֹהִים and the LXX rendering ὁ θεός)
psa-102-25-27 (Hebrew grammar of MT Psa 102:26 יָסַדְתָּ with implicit YHWH-addressee)
psa-2-7, psa-97-7, psa-104-4, psa-110-1, 2sa-7-14 (remaining six Heb 1:5-13 source passages)

Summary — Grammatical Findings¶

Heb 1:8 ὁ Θεός is an articular-nominative-as-address (vocative function, nominative form), not a nominative-of-predication. This is established by (a) standard LXX convention for rendering Hebrew vocative אֱלֹהִים, (b) the parallelism with the true vocative Κύριε in v.10, (c) the consistent 2ms σου-address chain running through vv.8-12, and (d) the contrast with v.9b's ὁ Θεός which IS nominative-of-subject for the verb ἔχρισέν.
Heb 1:10 Κύριε is a true morphological vocative, making the Son the explicit addressee of a text (Psa 102:25 LXX = 101:26) whose original addressee is YHWH.
The grammatical argument of Heb 1:5-13 transfers six pre-existing OT addresses/predications onto the Son — Davidic-messianic (Psa 2:7; 2 Sam 7:14), angel-worship (Deut 32:43 / Psa 97:7), divine-title (Psa 45:6), YHWH-creator (Psa 102:25), and YHWH-enthronement (Psa 110:1) — using grammatical forms (pronominal-chains, vocatives, 2ms-verbs) that survive the transposition intact.
The grammar itself does not adjudicate Christology — it supplies the forms within which the Hebrews author's argument runs. What the grammar does establish unambiguously is (a) the direct-address structure, (b) the morphological vocative at v.10, and (c) the explicit subject-predicate asymmetry between v.8's ὁ Θεός and v.9b's ὁ Θεός. All Christological interpretations of Heb 1:8-10 must accept those grammatical baselines.