Some context: Hilary Whitehall Putnam (; July 31, 1926 - March 13, 2016) was an American philosopher, mathematician, and computer scientist, and a major figure in analytic philosophy in the second half of the 20th century. He made significant contributions to philosophy of mind, philosophy of language, philosophy of mathematics, and philosophy of science. At the time of his death, Putnam was Cogan University Professor Emeritus at Harvard University. He was known for his willingness to apply an equal degree of scrutiny to his own philosophical positions as to those of others, subjecting each position to rigorous analysis until he exposed its flaws.
In the field of epistemology, Putnam is known for his "brain in a vat" thought experiment (a modernized version of Descartes's evil demon hypothesis). The argument is that one cannot coherently state that one is a disembodied "brain in a vat" placed there by some "mad scientist".  This follows from the causal theory of reference. Words always refer to the kinds of things they were coined to refer to, thus the kinds of things their user, or the user's ancestors, experienced. So, if some person, Mary, were a "brain in a vat", whose every experience is received through wiring and other gadgetry created by the "mad scientist", then Mary's idea of a "brain" would not refer to a "real" brain, since she and her linguistic community have never seen such a thing. Rather, she saw something that looked like a brain, but was actually an image fed to her through the wiring. Similarly, her idea of a "vat" would not refer to a "real" vat. So, if, as a brain in a vat, she were to say "I'm a brain in a vat", she would actually be saying "I'm a brain-image in a vat-image", which is incoherent. On the other hand, if she is not a brain in a vat, then saying that she is a brain in a vat is still incoherent, but now because she actually means the opposite. This is a form of epistemological externalism: knowledge or justification depends on factors outside the mind and is not solely determined internally.  Putnam has clarified that his real target in this argument was never skepticism, but metaphysical realism. Since realism of this kind assumes the existence of a gap between how man conceives the world and the way the world really is, skeptical scenarios such as this one (or Descartes' evil demon) present a formidable challenge. Putnam, by arguing that such a scenario is impossible, attempts to show that this notion of a gap between man's concept of the world and the way it is, is in itself absurd. Man cannot have a "God's eye" view of reality. He is limited to his conceptual schemes. Metaphysical realism is therefore false, according to Putnam.
How did it explain metaphysical realism?
A: such a scenario is impossible, attempts to show that this notion of a gap between man's concept of the world and the way it is, is in itself absurd.

Some context: Calvin Cordozar Broadus Jr. was born in Long Beach, California, the second of three sons. He was named after his stepfather, Calvin Cordozar Broadus Sr. His mother is Beverly Broadus (nee Tate). His father, Vernell Varnado, was a Vietnam veteran, singer, and mail carrier who was said to be frequently absent from his life.
Snoop signed with Master P's No Limit Records (distributed by Priority/EMI Records) in 1998 and debuted on the label with Da Game Is to Be Sold, Not to Be Told that year. His other albums from No Limit were No Limit Top Dogg in 1999 (selling over 1,503,865 copies) and Tha Last Meal in 2000 (selling over 2,000,000). In 1999, his autobiography, Tha Doggfather, was published.  In 2002, he released the album Paid tha Cost to Be da Bo$$, on Priority/Capitol/EMI, with it selling over 1,300,000 copies. The album featured the hit singles "From tha Chuuuch to da Palace" and "Beautiful", featuring guest vocals by Pharrell. By this stage in his career, Snoop Dogg had left behind his "gangster" image and embraced a "pimp" image.  In 2004, Snoop signed to Geffen Records/Star Trak Entertainment both of which were distributed through Interscope Records; Star Trak is headed by producer duo the Neptunes, which produced several tracks for Snoop's 2004 release R&G (Rhythm & Gangsta): The Masterpiece. "Drop It Like It's Hot" (featuring Pharrell), the first single released from the album, was a hit and became Snoop Dogg's first single to reach number one. His third release was "Signs", featuring Justin Timberlake and Charlie Wilson, which entered the UK chart at No. 2. This was his highest entry ever in the UK chart. The album sold 1,724,000 copies in the U.S. alone, and most of its singles were heavily played on radio and television. Snoop Dogg joined Warren G and Nate Dogg to form the group 213 and released album The Hard Way in 2004. Debuting at No.4 on the Billboard 200 and No.1 on the Top R&B/Hip-Hop Albums, it included single "Groupie Luv". Snoop Dogg appeared in the music video for Korn's "Twisted Transistor", along with fellow rappers Lil Jon, Xzibit, and David Banner,  Snoop Dogg's appeared on two tracks from Ice Cube's 2006 album Laugh Now, Cry Later, including the single "Go to Church", and on several tracks on Tha Dogg Pound's Cali Iz Active the same year. Also, his latest song, "Real Talk", was leaked over the Internet in the summer of 2006 and a video was later released on the Internet. "Real Talk" was a dedication to former Crips leader Stanley "Tookie" Williams and a diss to Arnold Schwarzenegger, the Governor of California. Two other singles on which Snoop made a guest performance were "Keep Bouncing" by Too $hort (also with will.i.am of the Black Eyed Peas) and "Gangsta Walk" by Coolio.  Snoop's 2006 album, Tha Blue Carpet Treatment, debuted on the Billboard 200 at No.5 and has sold over 850,000 copies. The album and the second single "That's That Shit" featuring R. Kelly were well received by critics. In the album, he collaborated in a video with E-40 and other West Coast rappers for his single "Candy (Drippin' Like Water)".
What success happened later on?
A:
The album sold 1,724,000 copies in the U.S. alone, and most of its singles were heavily played on radio and television.