The options in the grammar of a language derive from and are relatable to three very generalized functions of language which we have referred to as the ideational, the interpersonal and the textual. The specific options in meaning that are characteristic of particular social contexts and settings are expressed through the medium of grammatical and lexical selections that trace back to one or other of these three sources [...] the ideational [component], are concerned with the content of language, its function as a means of the expression of our experience, both of the external world and of the inner world of our own consciousness–-together with what is perhaps a separate sub-component expressing certain basic logical relations.
- Halliday (1973), a pag.66

The ideational component is that part of the grammar concerned with the expression of experience, including both the processes within and beyond the self---the phenomena of the external world and those of consciousness---and the logical relations deducible from them. The ideational component thus has two sub-components, the experential and the logical.
- Halliday (1973), a pag.99