The noble Shaykh, Muhammad ibn Saalih Ibn al-‘Uthaymeen – may Allaah raise his status among the guided ones, was asked about the meaning of Tawheed and its categories. He answered, saying:
Linguistically, Tawheed is the noun derived from the Arabic root verb: wahhada / yuwahhidu which means to make something one.
This is not accomplished except by a negation and affirmation, both together – negating this characteristic from anything other than the thing which is being singled out, and affirming it to that thing.
For example, we say that mankind will not fulfill the concept of Tawheed unless and until they testify that nothing deserves any form of worship except Allaah. By this, we negate any right of worship to anyone or anything other than Allaah (subhanahu wa ta’aala), and we affirm it to Allaah alone.
This is because negation alone equates to an absolute and complete negation, just as affirmation alone does not restrict others from sharing in the characteristic.
So if you were to say, “So and so is standing,” then you have affirmed that he is indeed standing but you have not singled him out alone, restricting this action only to him because it is possible, based on this saying alone, that someone else could also be standing with him. Similarly, if you were to say, “No one is standing,” then you have absolutely and completely negated the action of standing for anyone. However, if you said, “No one is standing except Zayd,” then you have singled out Zayd alone with the action of standing, negating it from anyone other than him. This is the true actualization of Tawheed in reality – meaning that Tawheed is not fulfilled unless it contains both negation and affirmation.
Posted from: Tawheed: Its Meaning and Categories – Shaykh Muhammad Ibn Sālih al-‘Uthaymīn [PDF] – Translated by Abu az-Zubayr Harrison @ authentic-translations.com