Article 19 of the Constitution provides: "The people shall have the duty to pay tax in accordance with the law." When the state levies income tax under the Income Tax Act, whether it be consolidated income tax payable by individuals or business income tax, every taxpayer is required to fill out an income tax return, file the form on his own initiative within the statutory time limit and present all account books, documents and vouchers that serve as proof of his income to enable the taxing authority to investigate and assess, upon receipt of the return, the amounts of income earned and the tax payable by him. Where a taxpayer fails to fill out and file a tax return within the statutory time limit or fails to present account books, documents and vouchers that serve as proof of his income during the taxing authority*s process of investigation or re-investigation, the taxing authority may determine his income on the basis of information obtained upon such investigation or the standard profits made by others in the same trade. Provisions to such effect are expressly set forth in the Income Tax Act, Article 71, Paragraph 1, first sentence; Article 76, Paragraph 1; Article 79, Paragraph 1; Article 80, Paragraph 1; and Article 83, Paragraph 1. This method of assessment by imputation does not contradict the purpose of the constitutional provision mentioned above. Nevertheless, when working on an estimate of the income by the method of imputation, the taxing authority must exert all possible efforts based on the rule of thumb (erfahrungsmäβig) to make an objective and reasonable estimation closely corresponding to the actual income of the taxpayer so as to safeguard the principle of fair taxation. As to the situation where an individual having sold a house fails to produce documents to prove the actual price of the deal at the time of the conclusion of the transaction and the actual cost of the original acquisition thereof, making it difficult to compute his income in the manner as specified in the Income Tax Act, Article 14, Paragraph 1, Category 7 (1), the Ministry of Finance Directives (67) Tai-Tsai-Shui-Tze No. 32252 issued on April 7, 1978, and (69) Tai-Tsai-Shui-Tze No. 33523 issued on May 2, 1980, state: "The income from property transaction shall be computed at 20% of the assessed value of the house in the year during which the house was sold." In other words, the amount of the taxpayer*s income is imputed at a fixed percentage of the assessed value of the house regardless of any variation due to year, location, and economic conditions. Nor is such formula designed for the purpose of discovering the true facts of the particular tax case. The resulting figure can hardly be expected to come close to the actual price and is unfair as well as unreasonable. Such a method is also inconsistent with the meaning of assessment by imputation as contemplated by the Income Tax Act and must cease to be operative within six months from the date of issue of this interpretation.