Common stock

Definition

Common stock is an ownership share in a corporation. A holder owns a proportional claim on the company’s residual assets and earnings, typically carries voting rights, and may receive dividends if the board declares them. Liability is limited to the amount invested; a shareholder cannot lose more than the position’s cost (unlike leveraged or short positions built on the stock).

How it works / structure

• Unit: one share; positions are integer share counts (some brokers offer fractional accounting, but the market trades whole shares).
• Cash flows: discretionary dividends (declared per share, paid on a schedule — see event-dividends-ex-dates); no maturity and no principal repayment.
• Price formation: continuous double-auction trading on exchanges during regular sessions, with opening/closing auctions (ms-sessions-auctions); price × shares outstanding = market capitalization.
• Rights: voting (usually one vote per share; dual-class structures differ), preemptive rights only if specified, residual claim junior to all debt and preferred stock in bankruptcy.
• Simulation parameters: entry/exit price series, dividend stream, share count; frictions per ms-bid-ask-spread and ms-slippage-friction; corporate-action adjustments per ms-corporate-actions.

When it applies

The default instrument for single-name fundamental, technical, and event theses, and the underlying for listed equity options. Long positions express appreciation and income theses; short positions (strategy-short-selling) express decline theses with materially different risk mechanics.

Risk profile & failure modes

• Full downside to zero: equity is the residual claim; in bankruptcy common holders are paid last and often receive nothing (per the SEC’s investor materials on stocks).
• Dividend risk: dividends are discretionary and can be cut to zero at any board meeting.
• Dilution: new issuance reduces existing holders’ proportional claim.
• Gap risk: single names jump on news across sessions; stops do not bound overnight moves.
• Delisting/halts: trading can be suspended (regulatory halts, exchange delisting), interrupting exit plans.

Evidence & limits

US equities in aggregate have historically returned more than short-term government debt by a margin large enough that Mehra and Prescott (1985) framed it as a puzzle for standard models — the canonical citation that an equity premium existed historically. Whether the forward-looking premium matches the historical one is unknowable in advance; entries never treat the historical premium as a promised return. Single-stock outcomes are far more dispersed than index outcomes; diversification math is covered in port-diversification-math.

Falsifiable-thesis examples

Illustrations only, not signals:

• “X will pay at least four quarterly dividends totaling $Y per share over the next 12 months” — falsified by any cut below that total.
• “X will outperform its sector ETF by 5% or more over the next two quarters” — falsified if relative return ends below +5%.

Cross-references

• Mechanics: ms-settlement, ms-sessions-auctions, ms-corporate-actions, ms-liquidity
• Derivatives on it: instrument-option-contract, ms-option-chain
• Strategies: strategy-buy-and-hold, strategy-dividend-income, strategy-short-selling
• Analysis: lens-fundamental, fa-financial-statements