企業的 CSR 投資常發生在市場看不見的地方。當消費者無法直接確認企業是否真的投入責任行為，而只能依據永續報告、第三方認證或其他公開資訊形成判斷時，產品市場獎勵的便不是真實投入本身，而是這些投入能否被轉化為可被相信的公開信念。本文建立一個三階段雙占模型，分析 CSR 投資、認證選擇、價格競爭與福利之間的關係。企業先選擇 CSR 投資以形成真實道德資本，接著決定是否參與認證；認證結果提供有資訊但不完全揭露的公開訊號，消費者據此形成可信道德資本，兩家企業最後在差異化產品市場中進行價格競爭。模型顯示，認證的經濟作用不只是揭露企業行為，而是使原本隱藏的 CSR 投入成為可被市場定價的差異化來源。當一家企業被市場相信具有較高道德資本時，它可以同時收取較高價格並取得較大的市場占有率；相反地，若真實 CSR 投資無法進入公開信念，便不會帶來價格與需求上的私人報酬。由於認證價值來自相對可信度差異，認證參與具有策略替代性，認證成本因而可使市場形成雙邊無認證、單邊認證或雙邊認證等不同配置。

不同認證配置進而重新塑造企業的 CSR 投資誘因。雙邊無認證下，投資無法被市場辨識，企業不會為產品市場報酬而投入 CSR；單邊認證下，只有認證方能將真實道德資本轉化為公開信念，因此認證方投資而未認證方不投資，且認證方個別投資高於對稱雙邊認證基準中的單一企業投資；雙邊認證下，兩家企業皆可被市場觀察，但 CSR 投資亦轉為相對可信度競爭，因而在局部上呈現策略替代。在公開信念下的產品市場福利基準中，更多認證或更高私人投資並不自動代表更高福利。單邊認證下，認證方存在局部投資不足；雙邊認證下，私人投資可能局部不足，也可能因相對可信度競爭使私人邊際收益高於社會邊際收益而局部過度。整體而言，本文說明 CSR 的市場價值取決於可信資訊制度。市場不會自動獎勵真實責任投入；只有當 CSR 投資透過認證形成可觀察、可比較且可被相信的公開信念時，才會成為產品市場中的有效競爭變數。

CSR investment often takes place in dimensions that consumers cannot directly observe. When consumers can only rely on sustainability reports, third-party certification, or other public information, the product market does not reward real effort itself. It rewards CSR only when real effort is transformed into credible public beliefs. This thesis develops a three-stage duopoly model to study the relationship among CSR investment, certification, price competition, and welfare. Firms first choose CSR investment, which generates true moral capital, and then decide whether to certify. Certification produces informative but imperfect public signals, from which consumers form credible moral capital. Firms finally compete in prices in a differentiated product market. The model shows that certification does more than disclose firm behavior. It turns hidden CSR investment into a form of differentiation that the market can price. A firm believed to have higher moral capital can charge a higher price and still attain a larger market share. By contrast, true CSR investment has no product-market return if it does not enter public beliefs. Because certification value comes from relative credibility, certification participation is strategically substitutable, and certification costs can support no-certification, unilateral-certification, or bilateral-certification configurations.

These certification configurations reshape CSR investment incentives. Without certification, investment is not recognized by the market, so firms have no product-market incentive to invest in CSR. Under unilateral certification, only the certified firm can transform true moral capital into public beliefs; the certified firm invests, the uncertified firm does not, and the certified firm's individual investment exceeds that of a single firm in the symmetric bilateral-certification benchmark. Under bilateral certification, both firms become observable to the market, but CSR investment also becomes a contest in relative credibility, making investments locally strategic substitutes. Under belief-based product-market welfare, more certification or higher private investment does not automatically imply higher welfare. Under unilateral certification, the certified firm locally underinvests in CSR. Under bilateral certification, private investment may be locally insufficient or locally excessive, depending on whether relative-credibility competition makes private marginal benefits fall below or exceed social marginal benefits. Overall, the thesis shows that the market value of CSR depends on credible information institutions. CSR becomes an effective competitive variable only when certification turns it into observable, comparable, and credible public beliefs.

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