The most difficult passages in Thucydides present themselves to the commentator like complex machines disassembled, without a set of instructions: the modern interpreter must examine each word, trying to determine not only how it fits with others but also its function for the whole, and as this becomes clearer he begins trying to put them together. Assembly is a slow process, and many lack the patience for it; they force the last few pieces, or even alter them to suit the places remaining. Finally, every assembler of Thucydidean sentences has had the disheartening experience of stepping back to admire his work only to discover a forgotten piece still lying by itself, indicating that the whole process must begin once again.