Why are junior soldiers called "privates"

[Rodney_of_Texas]

Where did the term “private” come from in ranking a junior enlisted soldier?

(or for that matter, “corporal” or “sergeant”)

Thanks.

[Exapno_Mapcase]

From this page.

Private comes from the Latin word privus or perhaps privo that meant an individual person and later an individual without (deprived of) an office. That certainly describes a Private in our Army or Marine Corps. The term as a military rank seems to come from the Sixteenth Century when individuals had the privilege of enlisting or making private contracts to serve as private soldiers in military units. Before the Sixteenth Century many armies were simply feudal levies in which the feudal lords forced their serfs or subjects to serve.

Go to that page and click on the links for corporal and sergeant for explanations of those terms.

[hammerbach]

That would be a “private soldier”, as one who is charged with duties pertaining only to himself, with no responsibility for any other (in other words, he has no other man to command or lead).