????投資往往為被描述為這樣一個過程，現在投入一些錢，希望未來能收回更多的錢。在伯克希爾哈撒韋（Berkshire Hathaway），我們采用更高的標準，將投資定義為“現在將購買力讓渡給他人，合理期待未來支付明義收益稅率后，仍能獲得更高的購買力”。簡言之，投資就是放棄現在的消費，以便將來有能力消費更多。

????從我們的定義可以得出一個重要結論：衡量投資風險高低的指標不應是貝塔值（一個基于波動率的華爾街術語，常用于衡量風險），而是持有期滿后投資人出現購買力損失的（合理）概率。資產價格可能大幅波動，但只要有理由肯定投資期滿后它們帶來的購買力能得到提升，這項投資就沒有風險。稍后我們還會看到，價格沒有波動的資產也可能充滿風險。

????投資選擇林林總總，但大體可分為三類，理解每一類的特點很重要。下面，我們將展開詳細的分析。

????市場上以特定貨幣結算的投資包括貨幣市場基金、債券、按揭、銀行存款和其他工具。大多數此類投資都被視為“安全”，但事實上卻是可能屬于最危險的資產。它們的貝塔值可能是零，但風險巨大。

????上個世紀，這類投資工具摧毀了很多國家投資者的購買力，盡管投資者一直能夠按時收到支付的本息。而且，這樣的糟糕結果將來還會不斷重現。政府決定貨幣的最終價值，而系統性力量有時會推動它們制定導致通脹的政策。這些政策一不留神就會失控。

????Investing is often described as the process of laying out money now in the expectation of receiving more money in the future. At Berkshire Hathaway (BRKA) we take a more demanding approach, defining investing as the transfer to others of purchasing power now with the reasoned expectation of receiving more purchasing power -- after taxes have been paid on nominal gains -- in the future. More succinctly, investing is forgoing consumption now in order to have the ability to consume more at a later date.

????From our definition there flows an important corollary: The riskiness of an investment is not measured by beta (a Wall Street term encompassing volatility and often used in measuring risk) but rather by the probability -- the reasoned probability -- of that investment causing its owner a loss of purchasing power over his contemplated holding period. Assets can fluctuate greatly in price and not be risky as long as they are reasonably certain to deliver increased purchasing power over their holding period. And as we will see, a nonfluctuating asset can be laden with risk.

????Investment possibilities are both many and varied. There are three major categories, however, and it's important to understand the characteristics of each. So let's survey the field.

????Investments that are denominated in a given currency include money-market funds, bonds, mortgages, bank deposits, and other instruments. Most of these currency-based investments are thought of as "safe." In truth they are among the most dangerous of assets. Their beta may be zero, but their risk is huge.

????Over the past century these instruments have destroyed the purchasing power of investors in many countries, even as these holders continued to receive timely payments of interest and principal. This ugly result, moreover, will forever recur. Governments determine the ultimate value of money, and systemic forces will sometimes cause them to gravitate to policies that produce inflation. From time to time such policies spin out of control.