A "captain" is a commander of a basic unit, a company in the military. As such, it makes sense that he will have one or more "lieutenants," first and second lieutenants that is.
A major commands the next higher level unit, a battalion. But there's no such thing as a "lieutenant major."
A colonel commands the next higher level unit, a regiment. He is two ranks above a major, with the intervening rank being a "lieutenant" colonel.
So why isn't a "first lieutenant" (second lowest commissioned officer) a captain, while a "captain" (the third lowest commissioned officer) a lieutenant major?
A "major (two star) general" commands the next higher unit, a divison. A one star general is a "brigadier general," who used to command a brigade, when there were four regiments in a division, meaning two regiments to a brigade and two brigades to a division. But when brigades were abolished, "brigadier general" lost its original meaning. Is he now a "lieutenant" major general?
A "lieutenant" (three star) general is one level below a "full" (four star) general. And a five star general is a "general of the army." Does this mean that a five star general is an army general, a four star general is a commander of a corps (the unit between a division and an army), and a three star general is a "lieutenant" corp commander?
Was it the original intent of the Anglo American armies to have "lieutenant" and then "full" officers at each level (captain, colonel, general, etc.)? Or if the ranks "evolved" over time, what was the history of the evolution?