There could be some doubt about the meaning of the word harpagmos if we looked only at the NT Greek Scriptures (since harpagmos occurs only at Phil. 2:6 in the entire New Testament). We would then only have the meaning of the source words for harpagmos to determine its intended meaning.
 "Either a reference to Christ's preexistence and those aspects of divinity that he was willing to give up in order to serve in human form, or to what the man Jesus refused to grasp at to attain divinity. Many see an allusion to the Genesis story: unlike Adam, Jesus, though . . . in the form of God (Genesis 1:26-27), did not reach out for equality with God, in contrast with the first Adam in Genesis 3:5-6."
The NASB, on the other hand, chooses an English word for harpagmos that doesn't clearly bring out its full intended meaning: "[Jesus] did not regard equality with God a thing to be grasped [harpagmos]," when, of course, it should be: "did not regard equality with God a thing to be taken by force [harpagmos]." (Review the quote from the Expositor's Greek Testament above.)
So when one thing is described as isa [ison] with another thing, they are still two separate different things. One is merely like or similar to another in a certain aspect.
Another thing we should know about Phil. 2:6, 7 concerns the phrase "of God" (θεοῦ or theou). A perfectly honest alternate translation of this verse can be: "though he was existing in the form of a god [i.e., `a mighty individual' in a similar sense that the Bible calls angels and Israelite judges `gods' - see the DEF and BOWGOD studies]." The NWT does not translate it that way, but grammatically and doctrinally it is a perfectly honest rendering and probably accounts for the 1959 French translation of Phil. 2:6, "being of divine status" and the NEB's "divine nature" and the renderings in Moffatt and the JB. (See the first part of the DEF study which discusses "god/divine.")
This scripture contrasts Jesus as, first, being in "form of god" (morphe theou) and, then, (2:7) being in "form of slave" (morphen doulou). Both of these phrases use the word "form" followed by an anarthrous genitive noun. This means that we are being given a contrast of two grammatical parallels.
If we should decide to translate the second half of this parallel as "form of a slave," then there can be no honest objection on grammatical grounds for translating the first part of this parallel as "form of a god." In fact it would seem more appropriate to translate it this way instead of "form of [the] God."
The Watchtower Society, however, interprets Phil. 2:6 to mean that Jesus was in the form of God. That is, he was a spirit person as are all heavenly persons - see WORSHIP-1. The Father is a spirit person (John 4:23, 24 KJV, ASV); the angels are spirit persons (Heb. 1:7 KJV - also see Aid book, p. 1542 - and pp. 39 and 593 in the trinitarian Today's Dictionary of the Bible); men resurrected to heaven become spirit persons (Phil. 3:20, 21; 1 Cor. 15:44-53); and Jesus is (and was in the beginning also) a spirit person (1 Pet. 3:18, 1 Cor. 15:45).
Although it has been rejected by even many trinitarian Bible scholars, some others attempt to force an interpretation of morphe (μορφῇ) that includes the idea of "essence" or "nature." They do this only at Phil. 2:6 (Jesus "was in the form [morphe] of God") because the true meaning of morphe will not allow for the trinitarian interpretation that Jesus is God. But with their forced interpretation of morphe at Phil. 2:6 they can say that Jesus had the "absolute essence" and "full nature" of God!
However, as even many trinitarian Bible scholars admit:
Phusis, "φύσις... nature, i.e, .... d. the sum of innate properties and powers by which one person differs from others" - Thayer, #5449.
Phusis, "φύσις, ... the nature, natural qualities, powers, constitution, condition, of a person or thing" - Liddell and Scott, p. 876.
Ousia, "οὐσία ... that which is one's own, one's substance, .... III. the being, essence, nature of a thing" - p. 579, Liddell and Scott's An Intermediate Greek-English Lexicon, Oxford Press.
For example, Philo, the most popular Jewish scholar and teacher of these times (early to middle first century A.D.), used these two terms in speaking of God's nature:
And when we know that `morphe of a servant' means `external appearance like that of a servant,' then we know that this morphe's parallel in `morphe of God' must mean an "external appearance like that of God (or `a god')"!
"[huparcho] ... to begin, make a beginning ... 2. to make a beginning of ... 3. to begin doing ... 4. to begin [doing] kindness to one ... Pass. to be begun" - p. 831, Oxford University Press, 1994 printing. 
In that sense, then, huparchon is very much like another NT word, ginomai, γινόμαι [#1096, Thayer's], which also literally means "become" or "come into existence" but is sometimes translated into English as "is," "are," etc. E.g., 1 Peter 3:6 "whose daughters ye are [ginomai]," KJV, NKJV, NAB, RSV, NIV, is more properly understood as "you have become [ginomai] her children," NASB, NRSV, NEB, NWT - Cf. John 6:17, "It was [ginomai] dark."
As respected trinitarian NT Greek expert Dr. Alfred Marshall tells us:
"But thanks be to God, who puts the same earnestness on your behalf in the heart of Titus. For he [Titus] ..., being [huparchon] himself very earnest, he has gone to you of his own accord." - NASB.
[To be honest, I must admit that a friend who is a NT Greek scholar disagrees with my understanding of huparchon. He believes that it is properly used as 'being' without regard to 'beginning.']
What we really have at Phil. 2:6-7, then, may be more accurately rendered:
Part 2 - Notes