As I am new to Ancient Greek you may find some imperfections in my personal transliteration of the value of the Greek sounds [letters] into an English rendering - if there are, I ask you to please be forbearing.)

 Greek philosophy or more properly Greek philosophers seldom severalise the differences between the existential and copulative operations of einai 'to be.' That is in their writings it is never quite clear as to whether the use of einai is to mean - in Aristotle's words - that an entity: “absolutely is, not is one of its attributes, or whether it is one of its attributes,” [Posterior Analytics.] for which alternative expressions of simple existence and existential modality or state in Modern English we would substitute the word “exists” or perhaps “essence.” The Greek word which can be said to be equivalent to 'being' in English is ousia, which in addition to its normal grammatical chores accommodates the semantic and grammatical categories later distinguished by the scholastic introductions - “essentia” and “substantia,” and which in the absence of such words Socrates, Plato, Aristotle and the rest, not to mention the pre-Socratics, were profoundly disadvantaged linguistically.

 In physics V. vii, he attempts to analyse and separate out being per accidens from being per se and categorises being per se into the well-known categories, which in my opinion are still valid and useful after a certain amount of updating in the light of later scientific discoveries, and in particular I offer my suggested nine existential modalities which are available elsewhere.

 The section of the Posterior Analytics is much more interesting to an ontologist in that Aristotle, at great periphrastic expense, tackles the question of ei esti and ti esti in more depth, and makes it quite clear to us exactly what the difference is between: “What it is,” and “ Whether it is,” (Whether it exists) It is much more difficult for him to explain this than one would imagine, for in spite of all that is said about the glory of the Greek language, they lacked two words which are essential for a clarity of expression regarding ontological communication, and that is that they had no word for “exist” or for “essence.”

 Look at the amount of periphrasis required to express indirectly simple existence:

 "I mean the question whether or not it is absolutely, not whether it is white or not" “d ei estin i mi aplos lego, all ouk ei lenkon i mi.”

 Labouring under this lack of suitable vocabulary to explain the ontological difference he believes exists between these two expressions, (of the fact that a entity exists, and the way in which it exists,) which are both signaled by the same word einai [with the same parisology to be found in its conjugate ousia] he is forced to go to extraordinary lengths to make it clear just what ontological meaning he intends when he tackles such questions that require semantic explicitness.

 He can distinguish between existential and copulative functions only by such formulaic mouthfuls as:

 "the substance being not this or that but absolutely, or not absolutely but something per se or per accidens" (… ton einai mi todi i todi all aplon thi ousian, i ton mi aplos alla ti ton kaf auto i kata sumbebikos. and "whether it absolutely is, not is one of its attributes, or whether it is one of its attributes" (i aplos kai mi ton uparhonton ti, I ton uparhonton.

(Posterior Analytics 89b 33.)

 Whenever Aristotle dispenses with such illuminatory constructions we are left in the dark again, and one of the difficulties in these situations for a translator is the inconceivableness of substituting einai with the inflexible English 'to be' and the temptation is (depending on the philosophical position of the translator) to evaluate beforehand, without sufficient evidence regarding the ontological ramifications and - if it suits your particular transcendentalist or analytical agenda - to stick in the modern word 'exist' or to slot in the dreaded “Being” word instead.

 Aristotle correctly confirms that distinctness or definition shows what a entity is (Ii esti) but not 'that it is' (hoti esti), which is known not by definition but by demonstration, the physically minded translator will not need much encouragement to render hoti esti with the medieval: 'existence,” wrongly jumping the gun by a thousand years or so, although it certainly embraces not only the existence [existing] of the said entity, but its being in fact what it is defined as being - which is the said entity.

 At first glance the problem seems to be that there hasn't been anything considered sufficiently interesting in physics to attract analytically minded translators into the field, and therefore the knowledge domain seems to have been left wide open to the metaphysical community without any monitor to report and flag-up any perceived excesses?

If this is not the case and there are in fact thousands of “alternative” or “realistically-based” or “logically-inspired” translations out there somewhere, then I would be more than happy to hear about them.