詐欺罪中不法所有意圖的由來、能發揮何種功能以及應該如何具體認定，一直以來在文獻上都算不上是討論的重點。早期學說多將之與竊盜罪的不法所有意圖相比較，實務上對於行為人是否具備詐欺罪不法所有意圖的認定標準亦流於恣意，對於意圖的內容與損害的發生也沒有詳加區別。事實上，詐欺罪中的不法所有意圖應有其獨自的地位與功能，性質上屬於一種「過剩的內心傾向」；詐欺罪的不法意圖能夠凸顯詐欺行為具有「財產移轉」、「不法獲利」、「同質性」與「截斷的結果犯」等等的特性，只有當我們能正確認識不法所有意圖所能發揮的作用時，我們才能適當地操作詐欺罪的構成要件；於此同時，我們可以有充足的理由認為刑法第339 條第2 項詐欺得利罪的規定沒有存在的必要。

The origin and functions of the illegal intent as well as its criterion were for a long time not focal point of the discussion between the scholars. The earlier opinion more often compares the intention of fraud with that of the theft. The criterion by which we investigate the intention of the offender is determined recklessly in the judicial decision. The content of the intention is not distinguished from the damage. In fact, the illegal intent of fraud should have its own position and functions. It has the feature as the ＂excessive internal tendency＂. The illegal intent can mark characters of fraud such as ＂fraudulent transfer of asset＂, ＂unjustified enrichment＂, ＂equality of substance＂, ＂type of objective crime in relation to which the intent to cause the resulting damage or harm does not have to continuously exist＂ etc. Only if we realize the functions of illegal intent correctly, we can handle the mental elements of fraud appropriate. Meanwhile it convinces us with good reasons, that Exist of paragraph 2 of Article 339 of Criminal Code is not necessary.