article The Four Levels of Forbidding Evil

Forbidding Evil has four levels:

The first: That the evil is removed and the opposite (good) takes its place.^[1]

The second: The evil is lessened but is not removed completely.^[2]

The third: The evil is replaced with what is similar/equal to it.^[3]

The fourth: The evil is replaced with something worse than it.^[4]

The first two levels are legislated (permitted), the third is an area of Ijtihaad and the fourth is prohibited.

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The following is only an example to clarify the meaning.

[1] A person is encouraged to abandon smoking cigarettes and burns incense in his home or drinks coffee in its place or just simply abandons smoking cigarettes.
[2] A person is encouraged to abandon smoking cigarettes and responds by smoking less often.
[3] A person is encouraged to abandon smoking cigarettes and consequently abandons it and replaces it with smoking Shihah (sometimes called hubbly bubbly).
[4] A person is encouraged to abandon smoking cigarettes and consequently abandons it and replaces it with smoking weed or other such substances.

This scenario can be visualized if a person were to be encouraged to abandon smoking by only citing its harmful effects on the body such as its effect on the lungs or the risk of cancer, he then figures that smoking weed which carries a more sever prohibition or Shisha which carries a similar prohibition are fine since they may not have those particular harmful effects on the body while he was unaware that they are prohibited from different angles.

There are many other examples that do not necessarily have to have a relation with each other such as the example used.