TL;DR: The double-entry bookkeeping system, the bedrock of modern accounting, was pioneered by Luca Pacioli, a close friend of Leonardo da Vinci. Understanding its core principle (Assets = Liabilities + Equity, and every transaction having equal Debit and Credit entries) isn't just for accountants; it's essential business "common sense" for everyone, including tech teams. It provides transparency, enables the concept of a company as a separate legal entity, and helps us understand our clients and the health of any business.
When you think of Leonardo da Vinci, you probably picture the Mona Lisa or incredible inventions. But did you know his influence might extend to the very foundation of modern business accounting? His close friend, the mathematician Luca Pacioli, is considered the father of modern accounting, largely for popularizing (and possibly inventing, perhaps inspired by da Vinci's ideas on duality) double-entry bookkeeping ("複式記賬法").
This system, born during the Italian Renaissance, is now the universal standard for financial recording worldwide. It underpins the key financial statements – the Balance Sheet, Income Statement, Cash Flow Statement, and Retained Earnings Statement – that aim to provide corporate transparency, verify business activities, and ensure efficient market function.
Why Programmers Need to Understand Debits and Credits
You might be surprised to learn that every new team member joining Mercury Technology Solution, regardless of their role, has a basic requirement: pass the LCCI Level 1 bookkeeping qualification within six months. They also need to grasp fundamental company law.
Initially, our programmers often question this. "Why do I need accounting?" But after they start interacting directly with clients, the lightbulb goes on. They realize that accounting and basic legal principles are the common sense, the fundamental language, of the business world. Understanding concepts like Assets, Liabilities, Debits, and Credits isn't just about balancing books; it's a powerful way to understand a client's situation, challenges, and how our solutions impact their financial health.
The Elegance of Double-Entry: A Simple Explanation
So, what is this system? At its heart lies the basic accounting equation:
Assets = Liabilities + Owner’s Equity
Let's break that down from the company's perspective:
- Assets: What the company currently owns or controls (cash, equipment, receivables, etc.).
- Liabilities: What the company owes to third parties (loans, supplier payments due, etc.).
- Owner’s Equity: What the owners have invested in the company (the company essentially "owes" this back to its owners).
The equation simply says: Everything the company has (Assets) had to come from somewhere – either it was funded by owners (Equity) or by borrowing/owing others (Liabilities).
Why the terms Debit (Dr) and Credit (Cr)? Their Latin roots offer a clue: Debit comes from debitum (debt), and Credit relates to trust or belief. From the company's viewpoint, all its assets represent obligations or "debts" – owed primarily to its owners (Equity) and potentially creditors (Liabilities). These parties provide funds because they trust (Credit) the company.
To account for ongoing business activity (making money, spending money), the equation expands slightly:
Assets + Expenses = Liabilities + Owner’s Equity + Revenue
Here’s the core rule of double-entry:
- Items on the left side (Assets, Expenses) increase with a Debit and decrease with a Credit.
- Items on the right side (Liabilities, Equity, Revenue) increase with a Credit and decrease with a Debit.
Crucially, every single transaction affects at least two accounts, and the total Debits must always equal the total Credits for that transaction. "有借必有貸，借貸必相等" (yau jeh bit yau taai, jeh taai bit seung dang) – Every debit must have a credit, and debits must equal credits.
Let’s look at some simple examples (using hypothetical numbers for my company):
- Founders invest $500k cash:
- Cash (Asset) increases: Debit $500k
- Owner's Equity increases: Credit $500k (Assets up = Equity up; Dr = Cr)
- Company buys servers for $50k cash:
- Fixed Assets (Asset) increase: Debit $50k
- Cash (Asset) decreases: Credit $50k (One asset up, another down; Dr = Cr)
- Company pays salaries of $50k cash:
- Salaries (Expense) increase: Debit $50k
- Cash (Asset) decreases: Credit $50k (Expense up = Asset down; Dr = Cr)
- Client pays $100k cash for services:
- Cash (Asset) increases: Debit $100k
- Revenue increases: Credit $100k (Asset up = Revenue up; Dr = Cr)
The 'Why': Separate Entity and Accurate Measurement
Why this seemingly complex system? It's fundamental to the concept of the company as a separate legal entity. We keep books from the company's perspective, distinct from its owners or creditors.
When resources flow in, the company's assets increase, but this inflow always corresponds to an increase in someone's claim on those assets – either the owners' (Equity) or creditors' (Liabilities). Double-entry tracks both the resource itself and its source or claim.
This separation is vital. It allows for limited liability – the company can potentially fail and go bankrupt, but because its debts are separate from the owners' personal debts (generally), the owners aren't usually personally liable. (Though illegally taking company assets is still a crime!). It also enables accurate measurement and reporting of profit and financial position at any point in time.
This ability to accurately track finances, enabled by double-entry, was a key underpinning of the commercial explosion during the Italian Renaissance and continues to support the entire global economy today. It brought mathematical rigor to commerce, just as da Vinci brought it to art.
Double-entry的發明 還要感謝達文西
現代會計的始祖是盧卡．帕喬利（Luca Pacioli），亦是達文西（Leonardo da Vinci）的密友。帕喬利受達文西二元論的啟發，發明 「複式記賬法」（Double-entry bookkeeping），是目前世界大部份國家的通用記賬方法，是會計入門。用這基本原則，每年經由會計而產生的公開財務報表，旨在保證公司的透明度，從而檢驗公司的行為，並確保市場有效運作。這些報表包括資產負債表（Balance Sheet）、損益表（Income Statement） 、現金流量表（Cash Flow Statement）和保留盈餘表（Retained Earnings Statement）。
所以每一位進入我公司成爲團員有一個基本要求，就是要在六個月內考到LCCI，瞭解公開財務報表及基本公司法。對所有剛進公司的Programmer，他們初期非常不理解，但和客戶對談後，他們才明白會計及法律知識就是商業世界的Common Sense。Accounting + Double-entry / Debit／Credit 亦是了解客户的一個方法。
複式簿記基本原則： 英文中Debit 的詞源是拉丁語的debitum，表示債務，而Credit的本意是信任，這兩者如何在會計聯繫呢？ 我們來看最基本的會計恆等式： Asset（資產） = Liability（負債） + Owner’s Equity（股東權益）
從公司本身的角度：資產表示當前在公司手上的東西，右邊表示這些東西從哪裡來，是屬於股東的還是第三方的。公司所有的資產，歸根到底都是這個機構的債務，首先是欠股東的（股東權益 Owner’s Equity），然後還可能欠銀行的，或者供貨商的 ( 負債 Liability）。股東和銀行為甚麽會願意借債給公司呢？因為信任（Credit）啊！ 所以Asset就是債務，而Liabitity + Equity 反映債權
中文中的借/貸為什麼沒有反映債務/債權的含義呢？ 因為這兩個字實際最早是日本人福澤諭吉的翻譯，他將Debit譯為「借りる」，縮寫為「借」；Credit譯作「貸す」，縮寫為「貸」；在日文裏前者表示「借來的」，即債務，後者「借給我的」，即債權，因此對日本人而言這兩個漢字的意義明確。但是被原封不動搬到中文就出事了。
因為公司是會賺錢也會虧本的，所以上述公式還可以擴展成這樣的形式 Asset（資產）+ Expense（費用） = Liability（負債） + Owner’s Equity（股東權益）+ Revenue （收入）
仔細觀察一下這個公式，會發現等式左邊表示錢/東西到哪裡去了；而右邊表示錢/東西從哪裡來的。 當左側增加，則記為Debit，減少的話記為Credit；右側正相反，增加的話記為Credit增加，減少則記為Debit。
公司的任何一筆涉及錢物的交易，分解到最基本的單元，都會最少記錄在兩個不同的會計賬戶（會計科目）當中，其中一個必定是Debit ，另一個是 Credit，因此記賬方法叫做複式記賬法。
我用我公司的經營活動來舉幾個例子（當然，以下數字都是虛構的）：
- 創始人共同投資了50萬，創建公司影響了Asset 和 Equity
- 公司現金資產增加50萬，Debit
- 股東權益增加50萬，Credit
- 公司購買了5萬元的服務器
- Asset中的現金減少，Credit
- Asset中的固定資產增加, Debit
- 公司給員工發了5萬元工資
- Asset中的現金減少，Credit
- Expense 增加，Debit
- 客戶給公司10萬元咨詢費用
- Asset中現金增加， Debit
- Revenue 增加， Credit
每一筆商業來往都要以相等的金額，同時在兩個帳戶中進行雙重登記，即有借必有貸，借貸必相等。
記賬的主體是「公司」，不是股東，也不是債權人（這就是公司的法人獨立性）。所以資源流入的時候，公司資產增加。但是「公司」 是屬於股東的，公司有一部分資產也是屬於債權人的，所以每一筆資源流入，必然對應股東權益增加，或者債權人債權增加；流出亦然。也就是說，公司每一筆業務導致的資源（財、物）流動，複式記賬法不僅給「主體」做了登記，還給資源的歸屬做了登記。
為什麼要這麼複雜？因為公司法人獨立，公司資產與股東財產分離，才能做到公司債務與股東責任分離。公司可以破產，因為經營的主體是「公司」而非股東個人，所以股東不必去還債；所以股東雖然是公司所有者，但是非法挪用公司財產照樣是犯罪。這個「主體觀」，不僅可以幫助理解復式記賬法，以後學習更複雜的企業合併、股權投資的有力工具。
商人就可以建立隨時結算的體系，即任何時候都可以算出一個利潤的準數。義大利在文藝復興時期的財富是靠著複式記賬法來支撐，當時一些頂尖畫家的藝術也是以數學來鞏固其基礎，從13世紀末的意大利，一直延伸到21世紀的全球經濟。
So, whether you're a programmer, marketer, designer, or CEO, taking the time to understand the fundamentals of double-entry bookkeeping isn't just an academic exercise. It's about learning the language that describes the health, performance, and structure of any business – including your own, and those of your clients. Understand the fundamentals.
