Greek philosophy ought to come with a warning label: “Objects may be farther than they appear.” Plato and Aristotle were so deeply influential that we use their philosophical vocabulary every day: Like them, we speak of causes and species, substance and essence, virtue and justice. Yet no sooner do we delve into a Platonic dialogue or an Aristotelean treatise than we realize that these deceptively familiar words are being used in very unfamiliar ways. To understand the Greeks involves a complex self-estrangement: We have to think ourselves out of our most basic assumptions about language, human nature, and the world. That is why the history of philosophy is not like the history of, say, warfare: To understand Julius Caesar it is not necessary to become a Roman general, but to understand Aristotle it is necessary to become, in a small way, a Greek thinker.

Who can we turn to for help in achieving this transformation? This is a very Socratic question: In Plato’s dialogues, Socrates is constantly trying to find out who has genuine knowledge or expertise – in Greek, techne – about matters of the spirit. When you want to sail a boat, Socrates is fond of pointing out, you ask a pilot; when you want to be cured of an illness, you ask a doctor. But who do you ask when you want to become good? The answer, at least in Plato’s early dialogues, is: no one. Socrates’s Athens was full of people who claimed to be experts on goodness and wisdom – everyone from poets to politicians to the freelance philosophers known as sophists. But Socrates was wiser than them all, the Delphic Oracle pronounced, because he alone knew that he was ignorant.

When it comes to the history of philosophy, surely the expert whose guidance we need is the professional philosopher. And Anthony Kenny, whose “Ancient Philosophy” (Oxford, 330 pages, $30) is the first of a planned four-volume history of Western philosophy, is as professional as they come: an expert on Aristotle and Aquinas, a former Master of Balliol and president of the British Academy. Yet while “Ancient Philosophy” proves Mr. Kenny’s erudition at every turn, the reader pays a price for this expertise.

Mr. Kenny’s lifelong immersion in the problems he discusses may actually leave him less than ideally suited to explain those problems to his declared audience – the novice reader and the beginning student. He is a good guide to individual philosophical debates, but not to larger philosophical contexts and worldviews. He communicates the difficulty of ancient philosophy, but not enough of its fascination and sublimity.

Perplexingly, Mr. Kenny chooses to omit things that, it would seem, any history of ancient philosophy must include. Plato’s parable of the Cave, for instance, is passed over in complete silence, even though it is probably the most famous image in all of Western philosophy. (It is mentioned once in the caption to an illustration.) Likewise, Mr. Kenny gives only a brief, almost mocking account of Plato’s metaphor, in the Phaedrus, of the soul as a chariot drawn by two horses, one obedient and one rebellious, and of his description, in the Symposium, of love as a ladder on which the soul ascends to the divine. It is no accident that it is Plato who suffers most from Mr. Kenny’s narrow-bore focus: An Aristotelean by trade, he is clearly impatient with the symbolic, dramatic, and poetic nature of Plato’s genius.

Mr. Kenny does excel in teasing out the implications of a knotty philosophical argument. His treatment of Aristotle’s logic is one of the book’s high points, making the subject as lucid as its difficulty permits. Likewise, he makes clear that many of the confusions of Greek philosophy can be traced back to the grammar of the Greek language. The centuries-long debate over the status of non-Being, which occupied every thinker from Parmenides and Democritus onward, was due in part to a failure to distinguish between Being and existence – a distinction easy to make in English, but highly elusive in Greek.

Even Mr. Kenny’s accounts of these subjects could have been made more accessible if his book were better organized. He begins by offering a brief, highly summary chronology of ancient philosophy, from the Pre-Socratics, through Plato and Aristotle, down to the Stoics and Epicureans, with a brief epilogue on the mysticism of Plotinus and the early, pre-Christian thought of Augustine. He then goes on to treat their thought at greater length in a series of thematic chapters – on logic, epistemology, physics, metaphysics, and so on.

This arrangement cuts against the grain of the subject, separating ideas and theories that belong together and could help to illuminate one another. Plato’s Cave, for instance, explains his epistemology, his metaphysics, and his ethics – all in a single luminous image. Likewise, Aristotle’s doctrine of substance and accident would be much easier to understand if presented all at once, rather than distributed over several chapters.

These objections do not diminish the authority of Mr. Kenny’s work. The next volume of his history, which will treat medieval Scholastic philosophy – the field of his own greatest contributions – is worth looking forward to. But they do make it questionable whether Mr. Kenny’s history of philosophy will become, as the publisher declares, “the definitive work for anyone interested” in the subject.