[4]The three fundamental obligations traditionally imposed on tacksmen were grassum (a premium payable on entering into a lease), rental (either in kind, or in money, which was designated "tack-duty"), and the rendering of military service.
To each of these brothers, nephews, cousins, and so forth, the chief assigned a portion of land, either during pleasure, or frequently in the form of a pledge, redeemable for a certain sum of money.
In the case of a very powerful chief, or of one who had an especial affection for a son or brother, a portion of land was assigned to a cadet in perpetuity; or he was perhaps settled in an appanage conquered from some other clan, or the tacksman acquired wealth and property by marriage, or by some exertion of his own.
In 1737, Archibald Campbell, 3rd Duke of Argyll decreed that tacks were to be let out to the highest bidder rather than being given to a tacksman with family connections, consequently many of the older sort of tacksmen were dispossessed.
Because they mustered the tenants, acted as officers and functioned as shock troops in time of war, Argyll had inadvertently weakened his military position and that of the Hanoverians in the 1745 Jacobite Rising.
To some, he appeared to be no more than a parasitic middleman, but Dr Johnson mounted a stout defence: To banish the tacksman is easy, to make a country plentiful by diminishing the people, is an expeditious mode of husbandry; but that abundance, which there is nobody to enjoy, contributes little to human happiness.