Lexicon

G1607 - ekporeuomai

Strong's: G1607 · BLB lookup Pronunciation: ek-por-yoo'-om-ahee Part of speech: verb, middle voice / deponent Root: ek, "out of", + poreuomai, "to go, to travel", so literally "to go out from" NT occurrences: about 30 verses, mostly ordinary movement (crowds going out to John, Matt 3:5; Jesus going out from Jericho, Matt 20:29), with three theologically weighted clusters treated below

Ekporeuomai is an ordinary verb of motion that one clause in John 15:26 turned into the most disputed technical term in the doctrine of God. The Niceno-Constantinopolitan Creed took its participle to name the Holy Spirit's eternal mode of origin, and the Greek and Latin churches have divided over what that word can and cannot say ever since. See Filioque.

Semantic range (Thayer / BDAG)

To go out, to depart from a place (Mark 10:46; Mark 13:1)
To come out of a source, of things issuing from the mouth or the heart (Matt 15:11; Mark 7:21)
To proceed, to issue forth, of what originates from someone (Matt 4:4; Rev 1:16; Rev 22:1)
To spread, of report or reputation (Luke 4:37)

The core image is constant: something has a source, and it comes out from that source. What the word does not by itself specify is whether the going-out is temporal or eternal, or whether it happens once or always. That underdetermination is exactly what the Trinitarian dispute exploits.

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The three weighted clusters

1. What comes out of a person, the heart-and-mouth sayings

It is not what enters into the mouth that defiles the man, but what proceeds out of the mouth, this defiles the man. (Matthew 15:11, NASB95)

For from within, out of the heart of men, proceed the evil thoughts, fornications, thefts, murders, adulteries. (Mark 7:21, NASB95)

The moral force of the verb is that it names origin, not merely location. What comes out of a person reveals what the person is. Compare Ephesians 4:29, where no unwholesome word is to proceed from the mouth.

2. What proceeds from God

Man shall not live on bread alone, but on every word that proceeds out of the mouth of God. (Matthew 4:4, NASB95)

Then he showed me a river of the water of life, clear as crystal, coming from the throne of God and of the Lamb. (Revelation 22:1, NASB95)

Revelation uses the verb repeatedly for what issues from the throne and from the mouth of the enthroned Christ (Rev 1:16; Rev 4:5; Rev 19:15), a divine-origin idiom the creedal use inherits.

3. The Spirit who proceeds from the Father

When the Helper comes, whom I will send to you from the Father, that is the Spirit of truth who proceeds from the Father, He will testify about Me. (John 15:26, NASB95)

The clause is ho para tou Patros ekporeuetai. Two things in it are load-bearing:

The verb is present indicative, not aorist. It is not a report of one past sending but of an ongoing or timeless relation, which is why the creed could read it as naming eternal origin rather than a historical mission.
The preposition shifts inside the same verse. The Son sends the Spirit para tou Patros, and the Spirit proceeds para tou Patros. The creed of 381 rewrote the phrase with ek, to ek tou Patros ekporeuomenon, "who proceeds out of the Father", which is a stronger origin-word than para ("from alongside").

The creedal and Filioque use

The Niceno-Constantinopolitan Creed (381) confesses the Spirit as to ek tou Patros ekporeuomenon. The Latin West rendered this qui ex Patre procedit and later interpolated Filioque, "and the Son".

The lexical core of the Eastern objection is a translation mismatch:

Greek theology reserved ekporeuesthai for origination from the ultimate source. In the Cappadocian grammar, the Father alone is aitia, cause, within the Godhead, so ekporeuesthai can take only the Father as its term. To say the Spirit ekporeuetai from the Son is, on that usage, a category error rather than a mere overstatement.
Latin procedere is broader. It translates both ekporeuesthai and the looser proienai, "to come forth", which Greek writers were willing to use of the Spirit's relation to the Son.

Maximus the Confessor made precisely this point in his Letter to Marinus (c. 645): the Latins, he argued, were not making the Son a second aitia; they were using a verb with a wider range, and their intent was expressible in Greek as dia tou Huiou, "through the Son". The 1995 Pontifical Council for Christian Unity document The Greek and Latin Traditions Regarding the Procession of the Holy Spirit reasons along the same lines.

The upshot for the apologist: the Filioque dispute is partly, though not entirely, a dispute about the semantic range of one Greek verb against one Latin verb. It is not resolved by lexicography alone, since a real theological question about the Father's monarchia remains, but any account of it that skips the lexical layer will misdescribe both sides. The full mapping is at Filioque.

Theological force

Procession is not creation. The verb names origin from a source of the same nature, parallel to the Son's begetting (gennaō) and unlike the making of a creature. This is the pneumatological half of the anti-Arian case and the ground of the Spirit's full deity confessed at Constantinople in 381.
Procession is not begetting. The tradition distinguishes the two modes of origin without claiming to explain the difference. Gregory of Nazianzus is candid about the limit: what the difference between generation and procession is, he says, we cannot say (Oration 31.8).
Relations of origin distinguish the Persons. The Father is unbegotten, the Son begotten, the Spirit proceeding. Nothing else distinguishes them, since the essence is one and undivided. See Relation (Thomist Metaphysics) and Monarchical Trinitarianism.

Notes

Lexical workspace for ekporeuomai.