The second dimension
Every lesson so far has treated price as the data. Price is the primary data — but it's not the whole picture. Every move on a chart is the result of someone buying from someone else, and volume is the count of those transactions. A 2% rally on a million shares means something different than a 2% rally on five thousand shares. Without volume, you're reading half the chart.
Murphy is explicit about the hierarchy:
Price is by far the most important. Volume and open interest are secondary in importance and are used primarily as confirming indicators. Of those two, volume is the more important. — John Murphy, Technical Analysis of the Financial Markets
And the why:
The level of volume measures the intensity or urgency behind the price move. Heavier volume reflects a higher degree of intensity or pressure.
Think of volume as a conviction index — not a direction signal, but a measure of how much the market cared about today's move. Price tells you where; volume tells you how much it mattered.
Dow's fifth tenet — the classical rule
From the Dow Theory lesson, verbatim:
Dow recognized volume as a secondary but important factor in confirming price signals. Simply stated, volume should expand or increase in the direction of the major trend. In a major uptrend, volume would then increase as prices move higher, and diminish as prices fall. In a downtrend, volume should increase as prices drop and diminish as they rally. — Murphy, paraphrasing Dow
Kaufman's compressed restatement:
Volume must increase as the trend develops, whether it is a bull or bear market. It is greatest at the peak of a bull market or during the panic phase of a bear market.
The rule in one line: volume should move with the trend. Divergence between volume and price — price making new extremes on thinning volume — is the first warning that the trend is tiring.
Three scenarios
Textbook Dow tenet #5 — volume expands in the direction of the trend, contracts on pullbacks. The impulse legs up show rising bars underneath; the short corrections come on softer volume. This is the pattern of participation: new money flowing in on every advance, sidelined on every pause. No warning signs.
Toggle the three examples:
- Healthy trend — volume expands on advance bars, contracts on pullbacks. The Dow tenet as it's supposed to look.
- Divergent warning — price prints new highs on declining volume. Effort is running out even as price keeps climbing. The breakdown at the end is confirmed by expanding volume, the other side of the same signal.
- Capitulation climax — the selling climax. A wide-range down-bar on 3–5× normal volume, closing well off the low. Every discouraged holder sells at the same moment; supply exhausts itself. The bounce and the low-volume retest complete the Wyckoff-style Phase A stopping action.
The asymmetry — volume matters more at bottoms
One under-taught subtlety. Volume behaves differently at tops vs bottoms. Murphy:
Markets have a tendency to 'fall of their own weight.' At bottoms, however, markets require a significant increase in buying pressure, reflected in greater volume, to launch a new bull market.
Tops can happen on drifting, unspectacular volume — the last buyer just stops buying. Bottoms require commitment — someone has to step in with real money to absorb the supply. That's why capitulation (climactic selling volume) is a high-probability bottoming signal, but "climactic buying" at tops is a rarer, weaker tell.
Practical consequence: if you see a 30% decline end on a wide-range bar with 4× average volume and the next day's bounce holds, something structural probably just happened. The symmetric "30% rally into a blowoff" happens too but you see it less often.
Effort versus result — Wyckoff's lens, Murphy's math
From the Wyckoff lesson: volume is effort, price change is result. Murphy translates the same idea into volume-confirmation rules. The clearest passage:
Divergence occurs if the penetration of a previous high by the price trend takes place on declining volume. This action alerts the chartist to diminishing buying pressure. — Murphy
Kaufman's four-way matrix is the most practical formalization:
| Price | Volume | Read |
|---|---|---|
| Rising | Rising | Bullish confirmation — advance has participation |
| Rising | Falling | Weak rally — new highs without new money; bearish divergence |
| Falling | Rising | Bearish confirmation — decline has urgency |
| Falling | Falling | Weak pullback — sellers exhausted; often sets up a bounce |
Murphy's deeper claim:
Technicians believe that volume precedes price, meaning that the loss of upside pressure in an uptrend or downside pressure in a downtrend actually shows up in the volume figures before it is manifested in a reversal of the price trend.
Whether "volume precedes price" is universally true is debatable (it's framework-dependent), but the operational rule — watch for price/volume divergence before price tells you directly — is high-value.
The breakout volume myth
Everyone's heard: "breakouts need heavy volume to be valid." Bulkowski tested this across 150,000+ patterns. The honest verdict, from his own book:
You will notice that the percentage difference is not great, especially after downward breakouts (which show ties). Breakout volume is not as good a predictor of performance as many believe.
The specific numbers: heavy vs light upward-breakout returns in bull markets were 43% vs 41% — a two-percentage-point edge. Statistically non-zero, practically not worth acting on. Bulkowski's personal view is blunter:
As a trader, I don't put much stock in volume. In fact, I prefer to look at charts without volume showing.
On the double-bottom myth specifically:
I have read that you should only buy double bottoms if the breakout occurs on heavy volume. Is that true? I don't think it's true. Volume (in other types of chart patterns) usually doesn't give the kind of boost many expect.
But — here's the nuance — intra-pattern volume contraction is statistically supported. Volume drying up during a consolidation is a real signal. Bulkowski on symmetrical triangles:
More than 80% of the triangles do show a receding volume trend, high enough to make you consider any deviations carefully.
Similar patterns show up in flags, rectangles, wedges, and cup-and-handle bases. The honest takeaway:
- Volume contracting inside a pattern → statistically real signal of declining supply/demand pressure
- Volume surge on breakout → weak predictor; don't filter trades on this alone
Murphy and Bulkowski disagree on breakout volume's importance. Our position: trust Bulkowski's data over Murphy's tradition here. The intra-pattern contraction is the signal; the breakout surge is narrative.
Volume spikes — the exhaustion signal
Kaufman's memorable framing of the capitulation-volume dynamic:
A volume spike means that everyone has jumped into the boat at the same time. Unfortunately, it indicates the end of a price move; that is, the boat sinks.
And his warning:
A volume spike does not indicate the strength of the price reversal; it simply tells you that the current move is exhausted.
Spikes signal exhaustion, not magnitude. A huge-volume climactic bar tells you "the current move is over" — it doesn't tell you whether what follows is a 2% bounce or a 50% rally. That's a separate determination.
Volume and Open Interest — futures only
A footnote for futures traders; equity traders can skip. Open interest is the total number of contracts outstanding (futures have no fixed float — every new buyer+seller pair creates a contract). Murphy's four reads:
| Trend | Open Interest | Read |
|---|---|---|
| Up | Rising | Bullish — new money fueling advance |
| Up | Falling | Bearish — rally is short-covering, not new buying |
| Down | Rising | Bearish — aggressive new shorts |
| Down | Falling | Bullish — longs forced out; downtrend losing fuel |
Useful if you trade futures. Irrelevant for stocks (where share count is fixed) and crypto (where OI is per-exchange-derivative, not spot-market).
What comes next — volume indicators
Eyeballing volume bars is imprecise. Murphy:
Technicians have experimented with many volume indicators to help quantify buying or selling pressure.
The main attempts:
- OBV (Granville, 1963) — accumulate signed volume (± based on close direction)
- A/D Line (Chaikin) — weight volume by close position within the day's range
- VWAP — volume-weighted average price over a session; the institutional benchmark
- Money Flow Index (Birinyi) — volume-weighted RSI
- Force Index (Elder) — price-change × volume
These all try to distill "how much buying pressure is there right now" into a single number. The next lesson covers OBV and A/D Line in depth; VWAP gets its own lesson after that.
Hidden traps
- Reading absolute volume, not relative. 10M shares on Amazon is normal; 10M on a thin small-cap is a 5× spike. Always compare to a moving average — Bulkowski uses 30-day.
- The intraday W-pattern. Volume is systematically higher at market open and close and lighter at midday (the "W" shape). Intraday volume reads must be compared to that time of day's normal, not the overall average.
- Thin stocks lie about volume. Kaufman: "Price changes that occur on very light volume are less dependable." A 5% move on 20 shares is nothing.
- Treating a spike as directional. Spikes signal exhaustion, not magnitude. They often precede a sharp reversal but don't predict how big it'll be.
- Expecting climax volume at every top. Tops often happen on quietly-declining volume — "falling of own weight" per Murphy. Climactic-volume blowoffs at tops are rarer than capitulation-volume climaxes at bottoms.
- Filtering breakouts on breakout volume alone. Bulkowski's data says the edge is ~2 percentage points. Not nothing, but don't bet the farm on a volume surge.
- Applying equity intuition to futures OI. OI mechanics are different. Stock traders should skip the four-read table; futures traders should memorize it.
Quick check
You see a stock print a new 52-week high today. Volume is 60% of the 30-day average. What's the correct read?
What you now know
- Volume is the second dimension of every chart — the intensity behind each move. Without it you're reading half the data.
- Dow's fifth tenet: volume should expand in the direction of the trend, contract against it.
- Volume/price divergence — price making new extremes on thinning volume — is the earliest warning that a trend is tiring.
- Kaufman's four-way matrix is the practical formalization: rising+rising bullish, rising+falling weak-rally, falling+rising bearish-confirm, falling+falling weak-pullback.
- Volume matters more at bottoms — markets can "fall of their own weight" at tops; bottoms require active buying commitment. Capitulation climaxes are higher-confidence than blowoff tops.
- Breakout volume is a weak predictor (Bulkowski: ~2 percentage points). Intra-pattern volume contraction is a real statistical signal (80%+ of symmetrical triangles).
- Volume spikes signal exhaustion, not magnitude — "everyone jumped into the boat at the same time" (Kaufman). They mark the end of the current move; they don't predict how big the reversal will be.
- Relative volume, not absolute. Compare to a moving average (Bulkowski uses 30-day), and account for intraday time-of-day patterns.
- Futures have open interest too — the four-read OI table is useful for futures, irrelevant for stocks.
Next: OBV & A/D Line — the two classic attempts to formalize volume pressure into a running number you can plot alongside price.