Praise be to Allah.

Firstly: 

We must understand the principle which says that there is nothing wrong with using new terminology. This principle is well-known among the fuqaha’ and scholars of usool. Ibn al-Qayyim (may Allaah have mercy on him) said: 

There is nothing wrong with new concepts and new words, unless there is something bad about them. 

Madaarij al-Saalikeen, 3/306 

Secondly: 

From early times the scholars have categorized the rulings of sharee’ah. This has only been done to make it easier to understand the texts and rulings of sharee’ah, especially as time goes by and knowledge of Arabic language becomes weaker and the language gets mixed with foreign languages. 

The scholars thought it wise to set out principles, issues and categories to make it easier to understand. There is nothing wrong with this, in fact it is a good thing because it makes knowledge more accessible to the Muslims. Al-Shaafa’i set out the principles of fiqh and his categorization was well-received and was followed by the scholars of usool who wrote commentaries on what he said and added to it. This was done in all branches of Islamic knowledge such as tajweed (recitation of Qur’aan), Qur’aan and others, including Tawheed. 

Thirdly: 

With regard to what the questioner mentions, that Shaykh al-Islam [Ibn Taymiyah] divided Tawheed into two categories and Shaykh Muhammad ibn Ibraaheem divided it into four, as did Shaykh Saalih al-Fawzaan, there is nothing wrong with that. We will explain this to you. 

Some of the scholars said that Tawheed can be divided into two categories: 

Tawheed al-Ma’rifah wa’l-Ithbaat (Oneness of knowledge and affirmation): which includes believing in the existence of Allaah and in His Lordship and His names and attributes. 

Tawheed al-Qasd wa’l-Talab (Oneness of object and aim), which includes believing in the divine nature of Allaah. 

With regard to those who divided Tawheed into three categories, they explained the previous categorization in more detail and made it easier to understand. So they said that Tawheed is divided into three categories: 

Tawheed al-Ruboobiyyah (Oneness of divine Lordship): which includes belief in the existence of Allaah. 

Tawheed al-Uloohiyyah (Oneness of the Divine nature) or Tawheed al-‘Ibaadah (Oneness of worship) – which mean the same thing. 

Tawheed al-Asma’ wa’l-Sifaat (Oneness of the Divine names and attributes) 

Then some of the scholars added to this categorization and said that Tawheed may be divided into four categories: 

Belief in the existence of Allaah. 

Belief in the Lordship of Allaah. 

Belief in the Divinity of Allaah. 

Belief in the names and attributes of Allaah. 

As we see, there is nothing wrong with this categorization as long as it does not point to anything false, and there is nothing wrong with the terminology. This categorization is only to make it easier to understand. The more time passes, the less people understand, and the scholars need to make things easier and simpler.  

To sum up, there is nothing wrong with what the questioner mentioned, because dividing Tawheed into two categories includes everything that is explained in detail by the others. Those who divided it into three or four categories explained in detail that which was mentioned in concise fashion by those who divided it into two. 

But all are agreed that Tawheed includes all the things that they mentioned.

There is nothing wrong with this categorization and this use of terminology, on condition that it does not lead to any problems, such as leaving out some of the concepts that are part of Tawheed, or introducing ideas that have nothing to do with it. 

There may come a time when it needs to be explained further, so the scholars will explain it with more categories in order to make it easier to understand. 

This is a brief explanation of what is meant by the three categories of Tawheed: 

Belief in Divine Lordship (ruboobiyyah): This means believing that Allaah is the only One Who creates, gives life and death, etc. 

Belief in the Divine nature (uloohiyyah): This means believing that Allaah is the only One Who to whom the people should devote their words and actions, both inward and outward. So none is to be worshipped but Him, may He be glorified and exalted. 

Belief in the names and attributes of Allaah (al-asma’ wa’l-sifaat): which means affirming what Allaah has affirmed for Himself of names and attributes, and denying any attributes that Allaah has said are not His, without denying any of His attributes or likening any of His attributes to the attributes of any of His creation. 

Fourthly: 

The scholars’ dividing Tawheed into these categories is nothing new, rather it was known in the third and fourth centuries AH, as was mentioned by Shaykh Bakr Abu Zayd, a member of the Council of Senior Scholars, in his book al-Radd ‘ala al-Mukhaalif.  This categorization was also narrated from Ibn Jareer al-Tabari and other scholars. 

Note: what the questioner mentioned, that Shaykh al-Islam Ibn Taymiyah divided Tawheed into two categories – Tawheed al-Ruboobiyyah (Oneness of divine Lordship) and Tawheed al-Asmaa’ wa’l-Sifaat (Oneness of the divine names and attributes) – is not correct. Rather he divided it into two categories which were Tawheed al-Ma’rifah wa’l-Ithbaat (Oneness of knowledge and affirmation) and Tawheed al-Qasd wa’l-Talab (Oneness of object and aim), the first of which includes Tawheed al-Ruboobiyyah and Tawheed al-Asma’ wa’l-Sifaat. 

See Majmoo’ al-Fataawa, 15/164; al-Fataawa al-Kubra, 5/250 

And Allaah knows best.