Regimental Proprietary System
The establishment of permanent units hastened the almost universal adoption of the proprietary system, which had already begun to replace the vestiges of feudalism and of free companies. The permanent colonel was the proprietor of his regiment, accepted by the king as a permanent officer and authorized (personally, and through him his captains) to raise men. Initially, with armies being raised only for a campaign and disbanded afterward, the troops raised by the proprietary system were volunteers, more or less carefully selected from the available and willing manpower. But as the armies became permanent, the standing units were not disbanded and were kept up to strength by regular influx of recruits, usually provided by the crown. This, combined with the financial considerations in maintaining year-round units, gave the crown increasing rights of supervision over the administration and training of the regiments, and thus somewhat restricted the proprietary right previously exercised by colonels and captains.This proprietary system could be profitable. A commander was paid for the number of men he mustered, as well as for their weapons, equipment, and subsistence. In addition to the profit to be derived from economical exercise of his proprietorship (to say nothing of the possibilities offered by parsimony and fraud), an officer could sell his proprietary interest when he retired. Thus officers’ commissions were valuable, and could be purchased. This custom of purchase of commissions continued in some armies—notably that of England—long after the proprietary system itself had disappeared.
— The Encyclopedia of Military History, p. 527