Herein references to living beings, gods, Brahma, etc., are sammuti-kathā [“relative truth”], whereas references to impermanence, suffering, egolessness, the aggregates of the empiric individuality, the spheres and elements of sense perception and mind-cognition, bases of mindfulness, right effort, etc., are paramattha-kathā ["highest truth"].
One who is capable of understanding and penetrating to the truth and hoisting the flag of Arahantship when the teaching is set out in terms of generally accepted conventions, to him the Buddha preaches the doctrine based on sammuti-kathā.
One who is capable of understanding and penetrating to the truth and hoisting the flag of Arahantship when the teaching is set out in terms of ultimate categories, to him the Buddha preaches the doctrine based on paramattha-kathā.
To one who is capable of awakening to the truth through sammuti-kathā , the teaching is not presented on the basis of paramattha-kathā, and conversely, to one who is capable of awakening to the truth through paramattha-kathā, the teaching is not presented on the basis of sammuti-kathā.
There is this simile on this matter: Just as a teacher of the three Vedas who is capable of explaining their meaning in different dialects might teach his pupils, adopting the particular dialect, which each pupil understands, even so the Buddha preaches the doctrine adopting, according to the suitability of the occasion, either the sammuti- or the paramattha-kathā.
It is by taking into consideration the ability of each individual to understand the Four Noble Truths, that the Buddha presents his teaching, either by way of sammuti, or by way of paramattha, or by way of both. Whatever the method adopted the purpose is the same, to show the way to Immortality through the analysis of mental and physical phenomena. AA. Vol. I, pp.54-55
What is interesting is to contrast this with Nagarjuna (MMK 24:8-11):
The Buddha’s teaching of the Dharma
Is based on two truths:
A truth of worldly convention
And an ultimate truth.
Those who do not understand
The distinction drawn between these two truths
Do not understand
The Buddha’s profound truth.
Without a foundation in the conventional truth
The significance of the ultimate cannot be taught.
Without understanding the significance of the ultimate
Liberation is not achieved.
By misperception of emptiness
A person of little intelligence is destroyed
Like a snake incorrectly seized
Or like a spell incorrectly cast.