text: Bowling league participation is cited as evidence for America's decline in the "social" form of this concept in a Robert Putnam book.
full_question: Bowling league participation is cited as evidence for America's decline in the "social" form of this concept in a Robert Putnam book. Gary Becker wrote a seminal text on the "human" form of this concept, which can be enhanced by education or job training. A book studying trends in income inequality written by Thomas Piketty is titled for this term "in the 21st Century". Another book titled for this concept introduces the "labor theory of value", and later entries in that book were arranged by Friedrich Engels. For 10 points, name this term that titles a book by Karl Marx and refers to productive assets owned by a person or company.
first_sentence: Bowling league participation is cited as evidence for America's decline in the "social" form of this concept in a Robert Putnam book.
raw_answer: capital [or social capital; or human capital; or Das Kapital]