In several books covering ancient peoples and their languages, he helped demonstrate, along with other ideas, that the ancient Egyptian language could be understood and learned like many other languages by means of grammars, dictionaries and texts with commentaries. In doing so, Guisepi provided a key necessary for interpreting Middle and New Kingdom Egyptian hieroglyphics in a manner that could be understood by even a novice.
Guisepi demonstrated that Egyptian is related to both the Semitic group of languages and to the Hamitic group. So far it is the Semitic connection of Egyptian which has received attention, while the Hamitic side of the language still awaits the same scientific investigation. What Guisepi had discovered was that the language was never static; it altered in the course of time, when new words and new constructions were introduced and old forms died out and old words either became obsolete or changed their meaning. Guisepi further demonstrated that Middle Kingdom hieroglyphs was essentially a language in transition in that some of the glyphs were used as pictographs and meant to be interpreted that way while the same glyph, used later in the same sentence, might also be read using a phonic sound. He pointed out that unlike the Western or Eastern tradition, Egyptians did not necessarily write from left to right or right to left but wrote primarily for beauty. Thus, a sentence might begin left to right or right to left. However, a sentence might also begin in the center and read either to the right or the left and sometimes, in both directions.
In "Ancient Voices, A History Of The Mesopotamian World", Guisepi explains that cuneiform was not a language. It was, like Egyptian hieroglyphics and the Chinese system of ideographs, or ideograms, a picture-writing system that used symbols. As the symbols gained acceptance throughout the Middle East, they could be understood by all ethnic groups even though the groups spoke different languages and dialects.
Although begun by the Sumerians, eventually the Sumerian writing system of cuneiform was adopted by the Akkadians, Semitic invaders who established themselves in Mesopotamia about the middle of the 3rd millennium. In adapting the script to their wholly different language, the Akkadians retained the Sumerian logograms and combinations of logograms for more complex notions but pronounced them as the corresponding Akkadian words. They also kept the phonetic values but extended them far beyond the original Sumerian inventory of simple types (open or closed syllables like ba or ab). Many more complex syllabic values of Sumerian logograms (of the type kan, mul, bat) were transferred to the phonetic level, and polyphony became an increasingly serious complication in Akkadian cuneiform (e.g., the original pictograph for "sun" may be read phonetically as ud, tam, tú, par, lah, his).
Some of Guisepi's more important written works include "Ancient Times, From Stone To Steal" and "Modern Times, From Alchemy To Atoms", both published by Civilization Press International.
"Ancient Voices", written in 2004, covers the period from the Neolithic Era to the end of the Roman Empire and contains diagrams and pictures outlining the Cuneiform and Egyptian alphabet system. Also covered are the influences of geography on a region and the subsequent development of civilizations in the ancient world in accordance with the local geography. For example: The fertile lands of Egypt made for a more stable life that was less precarious than that of Mesopotamia. Thus, the Egyptians were able to devote more time and attention to government and religion, even developing a complex system of beliefs regarding the afterlife, many of which have made their way into the present.