I disagree. 1. I can think of many bubbles that the author has lived through, even if he can't. Oklahoma natural gas in the early 1980s, junk bond credit bubb

I disagree. 1. I can think of many bubbles that the author has lived through, even if he can't. Oklahoma natural gas in the early 1980s, junk bond credit bubble in the mid 1980s, Japanese stock and property markets in the late 1980s, regionalized housing bubbles in California and Boston in the 1970s and 1980s, etc. There are many other examples, depending on how old he is (Nifty 50 in the late 1960s), etc. And I don't think it's a stretch to call the "mania" for tech stocks in 1999 a bubble. (If that's not, why is housing/credit in the 2000's a bubble?) Ignorance of history is not generally a qualification to opine on it. 2. To take this seriously as comment, he'd need to define the difference between a bubble, a mania, and a phenomenon, at least well enough for someone else to apply it to a situation and arrive at the same classification. Otherwise, this is an article about how he doesn't think there's a bubble, so you shouldn't either. 3. I will do him one better and hazard at least a partial definition of a bubble--a rapid and escalating series of price increases that is driven by a feedback loop of public perception rather than by the fundamental cash flows of the asset. One can quibble with this (it's hardly scientific). If you don't like mine, have a look at Robert Shiller's (http://dealbook.nytimes.com/2010/01/27/schillers-list-how-to-diagnose-the-next-bubble/ http://dealbook.nytimes.com/2010/01/27/schillers-list-how-to...). 4. To establish that this is not a bubble, he would need to make it clear why he believes that the cash flows the affected firms will ultimately generate will make their present valuations reasonable. While that may be true in some cases, in general I don't think it's a hard case to make that the tech industry has jumped from cyclical upswing to nascent bubble. Pockets of tech financing--arguably angel financing and some late-stage financing--are, to my eyes, pretty much already there.