What Does The Number 420 Signify, And Why?

420 is a slang reference to marijuana possesion.

It is not the number of chemicals in marijuana (315), tea time in Amsterdam (5:30), or a police code or criminal code anywhere. (For instance, California Penal Code 420 defines as a misdemeanor the hindrance of use ("obstructing entry") of public lands, and California Family Code 420 defines what constitutes a wedding ceremony. One state does come close: The Illinois Department of Revenue classifies the Alcoholic Liquor Act under Section 420; the Cannabis and Controlled Substances Tax Act are next, under Part 428.)

The evidenced etymological origin for the slang reference is a group of San Rafael teens in the 1970s ("the Waldos") who met at a statue of Louis Pasteur at 4:20 to smoke pot, said "420 Louis" to each other in passing, and have postmarked letters from the time period with many mentions of 420. (Maria Alicia Gaura for the San Francisco Chronicle, 4/20/00 p.A19)

But their choice of the time was not arbitrary, and the number has earlier meanings. It appears, inexplicably, in many 1960s songs (Dylan, CSNY, etc.), but also in "four and twenty black birds baked in a pie", the "four and twenty elders" in the book of Revalations, and elsewhere. In Midnight's Children, Salman Rushdie wrote, "...420 has been, since time immemorial, the number associated with fraud, deception and trickery." Besides. the hands on an analog clock at 4:20 look like a doobie dangling from a mouth. Plus April 20th was the copyright date for the propoganda film Reefer Madness (1936), the birthday of Surrealist painter Milo (1893), and the date Albert (not Abbie) Hoffman first encountered LSD. And one study purported to find that the effects of marijuana last for 4 hours and 20 seconds, with onset in the first ten minutes, "coming up" for 5-10 minus, a plateau for 15-30, "coming down" for 45-60 minutes, and "after effects" for 30-60 minutes, with a graphic summarizing the arc of a high.

Regardless of why the Waldos picked it, or who celebrated (or reviled it) first, the number became nationally popularized in the late 1990s as a colloquial reference not only to pot consumption but also a "good time" more generally. It is celebrated and noted by time (4:20 a.m. or p.m.), date (April 20th), or in any other instance (e.g. State Route 420). April 20th at 4:20 is marked by annual events in Mount Tamalpais, CA (an informal gathering); Marin Conty, CA (the 420 Hemp Fest); Ann Arbor, MI (the Hash Bash); and Washington, D.C. (buildup towards the July 4th Smoke-In). 

The number appears frequenty in popular culture - as well as in Phish history...

• Phish 3D (the movie) had a special preview screening on 4/20/10.
• The official logo includes 4 gills and 20 bubbles.
• Lawnboy is 420megs of memory.
• "The Vibration of Life" underlies a whirling loop with Seven Beats per second (which makes 420 beats per minute.)
• At the fall '94 Olympia show, there was a big clock tower with three sides giving the correct time and one stuck on 4:20.
• An uproar at 12/31/96 can be heard during the 2001 in response to an enormous digital clock (which was counting down to midnight) reaching 11:55:40 and reading "-4:20".
• For the summer 1997 tour, TicketMaster service charges were $4.20.
• The first day of the Great Went started at 4:20 (with Makisupa Policeman. (The second day started late, at 4:37.) Noah Cole
• Loring Air Force base (home of Lemonwheel and The Great Went) is 420 miles from Boston (former home of Phish).
• In the Fall 1997 Doniac Schvice Dry Goods section, a limited edition Pollack poster printed on 100% hemp is order number 420P.
• The first single from Slip Stitch and Pass was played on WBCN 10/14/97 at 4:20 pm.
• Trey has used the altered line "woke up at 4:20" in "Makisupa Policeman", which also often indirectly celebrates 420ing, e.g. by mention of goo balls.
• The first Mass Pike toll leaving Oswego was $4.20. 
• During the "2001" on 9-12-00, Trey hits the first riff right at 4:20 into the intro jam.
• Standard shipping for The Phish Companion through Amazon was originally $4.20.
• The Rolling Stone with Phish on the cover (2/03) cost $4.20 in PA.
• The title track for Trey's "solo" album Plasma clocks it at 4:20.
• The Jazzfest Harry Hood 4/26/96 started at about 4:20.
• At Big Cypress, "David Bowie" was playing at 4:20 a.m.
• The one event during the "hiatus" featuring all four members - for Jason Colton's wedding - was 12/1/01, 420 days after the hiatus began. 
• The first day of the Great Went started at 4:20, although that was called a soundcheck by Trey after three songs.

420 Shows: Phish performed on April 20 in 1989, 1990, 1991, 1993, and 1994.