Dow Theory: The Foundation
Charles Dow's original framework — the one nearly every later technical concept in the book traces back to.
Murphy treats Dow Theory, developed by Charles Dow around the turn of the 20th century and later formalized by others, as the direct ancestor of almost every concept covered later in the book — trend identification, the idea that averages must confirm each other, and the use of volume as a secondary confirming signal all trace back to it. The theory holds that the market moves in three simultaneous trends of different length: a primary trend lasting a year or more, a secondary (or intermediate) trend that corrects part of the primary trend and lasts weeks to months, and minor day-to-day fluctuations that Dow considered largely noise.
A second core Dow Theory tenet, confirmation, holds that a signal in one market average is only meaningful if a related average confirms it — originally, Dow required the Industrial and Rail averages to both make new highs (or both new lows) before a trend change was considered valid; a move in only one was treated as suspect. The theory also holds that volume should expand in the direction of the primary trend and contract on corrective moves against it — a thread Murphy picks back up in full in the volume chapter later in this course.
A third tenet, less quoted but equally load-bearing, is that a trend is assumed to remain in effect until a clear, decisive reversal signal appears — the burden of proof sits with the reversal, not with the trend continuing. This is a deliberately conservative default: it means a Dow theorist stays with an existing primary trend through ordinary secondary corrections rather than treating every pullback as a potential trend change, which is precisely the objective test the next chapter in this course formalizes into higher-highs/higher-lows trend identification.
Dow's original insistence that two separate averages confirm each other before a signal is trusted is presented as the theory's most durable idea, independent of which specific averages a trader actually watches today. The logic doesn't depend on the Industrial and Rail averages specifically — it depends on the principle that a genuine, broad shift in market direction should show up in more than one place, while a move confined to a single narrow average is more likely to be a false signal, sector-specific noise, or an anomaly in that one index rather than a real trend change worth acting on.
Confirmation is also, in effect, an early form of the same discipline that runs through every later chapter in this course: no single tool or signal, examined alone, is trusted as much as the same signal appearing in two independent places at once. Chart patterns get confirmed by volume, moving-average crossovers get confirmed by trend context, oscillator readings get confirmed by divergence checks — the specific mechanics change chapter to chapter, but the underlying instinct to demand agreement between two independent pieces of evidence before acting traces directly back to this original Dow requirement.
A modern equivalent: a trader today might require both a broad index and a related sector or breadth measure to confirm a signal before trusting it, the same non-confirmation logic Dow applied to the Industrials and Rails a century earlier.
A frequent criticism of Dow Theory is that its signals arrive well after a major turn has already begun — by the time both averages have confirmed a new primary trend, a meaningful portion of the move is typically already over. Murphy doesn't dispute this; he reframes it. Dow Theory was never designed to catch the exact top or bottom — it was designed to reliably identify the middle of a major trend while filtering out the much larger number of false starts and minor wiggles that a more sensitive, faster-reacting method would get whipsawed by.
This exact tradeoff — later confirmation in exchange for fewer false signals — reappears, in a more mathematically explicit form, in the moving-average crossover chapter later in this course, which makes essentially the same choice for essentially the same reason. Dow Theory is, in that sense, the conceptual ancestor of every lagging-but-reliable trend tool covered later in the book, not a separate, outdated idea sitting apart from them.
- Dow Theory identifies three simultaneous trend lengths — primary, secondary, and minor — with the primary trend as the dominant direction to trade with.
- A trend is assumed to remain in effect until a decisive reversal signal appears — the burden of proof sits with the reversal, not with trend continuation.
- Confirmation — requiring a related average or measure to agree before trusting a signal — is presented as the theory's most durable and still-relevant idea.
- Volume should expand with the primary trend and contract on corrections against it, a principle this course returns to directly in the volume chapter.
- Dow Theory's signals are inherently late — a deliberate tradeoff for fewer false signals that the moving-average chapter later in this course makes again in more explicit, mathematical form.