It is because people always tend to consider only primary...

It is because people always tend to consider only primary laws as the divine laws of Islam, without knowing that the secondary laws enacted for special conditions are also treated as religious laws. Islam also has a set of other laws that are called “secondary laws” and related to emergency cases and special conditions. Some of these secondary laws are also mentioned in the Book and Sunnah while others are mentioned in other religious sources.

To enact them is under the discretion of the wali al-amr al-muslimin . For example, it is obligatory upon us to perform ablution [ wudhu ] before saying our prayers. If bathing [ ghusl ] is wajib for us before prayer, then we have to perform ghusl . The obligatory nature of wudhu and ghusl is part of the primary laws for common situations when our bodies are physically sound and water is not harmful for us and there is available water.

But under exceptional situations when, because of ailment, we cannot perform ablution as water is harmful to our health, or we have no access to water, to perform dry ablution [ tayammum ] shall become wajib in lieu of wudhu and ghusl as a secondary law. For this reason, it is said that if you have no access to water or if water is harmful to your health, tayammum is regarded as the emergency substitute of wudhu and ghusl .

Once the primary laws and also the secondary laws which are likewise called “emergency laws” are mentioned in the Qur’an and traditions, we cannot observe any difference between them because in practice, the subject of the primary law, like wudhu and ghusl, is one who has access to water and to whose health water is not harmful, while the subject of the secondary law, like tayammum, is one who has no access to water and to whose health water is harmful.

As such, some people are commanded to perform ablution and others are commanded to perform dry ablution. In some cases, however, opposite to the primary laws are special laws that are suitable to exceptional and emergency situations and not particularly mentioned by religion.