An investment philosophy is a coherent, durable belief about where returns come from and why — the lens an investor uses to decide what to own, when, and for how long. This section maps the major schools: the deep-fundamental approaches (value, growth, GARP, quality, dividend/income), the empirical-factor approaches (momentum, contrarian), the structural approaches (passive indexing, special situations, activism), and the thematic/values-driven overlays (megatrend, ESG). Their core tension is that they make incompatible foundational claims about market efficiency — the value investor believes price routinely diverges from worth and can be appraised; the passive indexer believes the market's aggregate price is the best available estimate and tries only to capture it at lowest cost; the momentum investor believes recent prices themselves carry information. They cannot all be fully right at once, yet several have decades of evidence behind them. A philosophy is most useful precisely as a commitment device: a pre-chosen frame that keeps an investor disciplined through the long stretches when their style is out of favour.

The major schools (map of this section)

The children below are grouped by what they believe the source of edge is. Each has its own node — go there for mechanics, formulas, and measured base rates; this overview only situates them.

Fundamental / intrinsic-value schools — edge comes from appraising a business better than the crowd:

• Value investing (001) — buy below conservatively appraised worth. Subtopics: margin of safety, intrinsic value, deep value / net-nets, Graham vs Buffett approaches.
• Growth investing (002) — pay for above-average future earnings expansion. Subtopics: identifying secular growth, reinvestment runways, paying up for quality, growth-trap risks.
• GARP (003) — a hybrid that demands growth and a sane valuation (the Lynch/PEG school).
• Quality investing (004) — own durable, high-return-on-capital compounders. Subtopics: defining quality, high-ROIC compounders, durable competitive advantage.
• Dividend / income investing (005) — returns from cash distributions and their growth. Subtopics: dividend-growth investing, high-yield investing, payout ratio & coverage, dividend aristocrats, REITs for income.

Empirical / behavioural-factor schools — edge comes from a documented return pattern, not a business appraisal:

• Momentum investing (006) — recent relative winners tend to keep winning over 3–12 months (the Jegadeesh-Titman factor). Note the node's caveat: the portfolio factor is robust; a single hot chart is not.
• Contrarian investing (007) — fade crowd extremes and long-horizon overreaction (the De Bondt-Thaler reversal). It is, in effect, the mean-reverting mirror of momentum and of value.

Structural / mechanism schools — edge (or the deliberate refusal to seek one) comes from market structure:

• Passive / index investing (008) — don't seek edge; capture the market cheaply. Backed by Sharpe's arithmetic and the SPIVA record; now the majority of US equity-fund assets.
• Activist investing (009) — take a stake and force corporate change to unlock value.
• Special situations / event-driven (012) — returns tied to a discrete corporate event, largely decoupled from market direction. Subtopics: merger arbitrage, spin-offs, restructurings & distressed, IPOs & SPACs, activist catalysts.

Thematic / values overlays — selection organised around a narrative or constraint rather than a single financial metric:

• Thematic & megatrend investing (010) — express a long-duration structural trend. Subtopics: identifying durable themes, avoiding hype cycles, picks-and-shovels plays.
• ESG & sustainable investing (011) — layer environmental, social and governance criteria onto selection.

The core tension: efficiency, style cycles, and the factor zoo

These philosophies are not all rivals; many are facets of the same empirical research programme. Academic finance has catalogued a large and growing set of return "factors" — the factor zoo, with literature documenting on the order of several hundred candidate factors, though only a handful (market, size, value, momentum, profitability/quality) survive rigorous out-of-sample and multiple-testing scrutiny (AlphaArchitect; Springer/JBE factor-zoo review). Value, momentum and quality are the three that map most cleanly onto named philosophies, and a key practitioner finding is that they are imperfectly correlated — value and momentum in particular tend to be strongly negatively correlated — so combining them smooths returns across regimes rather than relying on one driver (AQR).

The second unifying truth is style cyclicality. No philosophy outperforms continuously; each endures multi-year stretches of underperformance tied to macro regime. Fama-French data show value has outperformed growth cumulatively over the long run yet suffered a punishing drought of roughly 2007–2020, with style leadership tracking interest-rate and inflation cycles that play out over years, not months (J.P. Morgan AM; Vanguard). This is why a philosophy's chief value is behavioural: it pre-commits the investor to a frame so they don't abandon it at the bottom of its cycle (the classic mistake of chasing whatever just worked).

When it matters vs not

Philosophy is load-bearing for capital-allocation, multi-quarter-to-multi-year horizon decisions — what to own and why. It is largely orthogonal to short-horizon, technical, swing-trade entry timing: knowing a stock is a quality compounder or sits below intrinsic value says little about whether today is a good entry, and several nodes (e.g. margin of safety) explicitly warn against treating a slow fundamental estimate as a timing trigger. The schools also differ sharply in who they suit — passive indexing is the rational default for an investor without an identified, cost-surviving edge, while the active schools are only justified if such an edge plausibly exists.

Sources

• AlphaArchitect — "The Factor Zoo Has Hundreds of Animals But Only a Handful of Species" (factor-zoo scale; surviving factors)
• Navigating the Factor Zoo Around the World (Journal of Business Economics, Springer) (institutional factor landscape)
• AQR — Understanding Factor Investing (value/momentum/quality correlations, multi-factor rationale)
• J.P. Morgan AM — Value vs Growth: A Historical Overview (style cyclicality, rate/inflation drivers)
• Vanguard — Value versus Growth Stocks (long-run value premium, ~2007–2020 drought)
• CFA Institute — Revisiting the Factor Zoo: time-horizon effects (horizon dependence of factors)
• Sibling child nodes in this section (value, growth, GARP, quality, dividend/income, momentum, contrarian, passive, activist, thematic, ESG, special situations) — go there for mechanics and measured base rates.

Disputes flagged: which factors are "real" vs data-mined artefacts of the factor zoo is genuinely contested; the value premium's long-run existence is well documented but its recent decade was negative and its risk-vs-behavioural cause remains unresolved. The relative merit of any philosophy is regime-dependent and not settled.