When Rousseau wrote his social theory, concepts of liberty and freedom were not new ideas. Hints of social contract reasoning are found in earlier works, most notably in Book 2 of Plato's dialog The Republic, as well as, in Socrates.
The total spending per iTunes account is $43 per year across all media, says Dediu. At 575 million iTunes accounts, that works out to $24.7 billion of consumer spending at iTunes per year. The average iTunes account's annual spending on software has followed music's trend, falling to $9 from $42 in 2008. However, average annual spending on apps has gone in the opposite direction, rising to $16 this year from $7 in 2008.
If you choose Account > View my Account in iTunes, iTunes will tell you how many Computer Authorizations you have. This number is the number of Macs or PCs that have explicitly authorized iTunes. To authorize or deauthorize your Mac, look at the Account: Authorizations submenu.