If you want a real in depth answer or study on "suchness" go to this web page....there is a pdf file at the bottom to get the whole piece...
Here is the beginning of the thesis.....
(1) Tathata in the Tripitaka, the Buddhist Scriptures and commentaries enables the students to understand that all the compounded things, which are called Five Aggregates. :- (corporeality, feeling, perception, mental formations and consciousness) and the non-conscious matters are Tathata. It means that nobody can change the law of nature. Under the law of nature all things are compounded and must be changed by the law of three characteristics. (Impermanence, State of Suffering, Not-self) Under the law of the three characteristics a thing arises in the primary state, changes in the middle and extinguishes in the end.
The synonyms of the term Tathata, are Avitathata which means certainty, Anannathata which means not being otherwise, Idappaccayata which means all the compuounded things arise from specific conditionality. All these synonyms mean that nothing can arise without any cause and there is nobody to create them. it arises according to its causes and factors.
In addition, Tathata is the wisdom arising to the person who practises insight meditation. It is he who can attain the insight knowledge of the conditioned state of things without their own personal ideas. Thus, the practiser can know that Five Aggregates are of non-essence and not to be attached to. They are always imcomplete, fearful, disadvantageous and full of suffering. Having seen all these conditions, the practiser is bored of all compounded things, has no pleasure in them and finally wishes to be away from them. Besides, he is so impartial that he can be free from the compounded things. this state is called Pannavimutti (Liberation through wisdom). This state is compared with the water on the lotus leaf. It is really called "Nibbana" which is "Asankhatadhamma" meaning the Unconditioned State. This is also called Tathata. In conclusion, both the conditioned state and the unconditioned state are Tathata.
(2) In the Buddhadasa Bhikkhu's thought, Tathata is "Suchness" which means the state of being so and not being other things, and no one can force it. It isas it used to be all the time. Such the state is surely called "Tathata." The explanation of Tathata by Buddhadasa Bhikkhu in another way is exactly the explanation of the Idappaccayata (specific confitionality) and of the Paticcasamuppada (Dependent Origination Law). These are the laws of reasons. (When there is this, there is that.) He explained that when there is no essence of the confitioned things, there is the impermanence and the change. But such change is in a similar line forever. That is called "Tathata".
Tathata in the Buddhadasa Bhikkhu's thought is not different from what is found in the scriptures. It is really the synonym for the words "Idappaccayata" and "Paticcasamuppada."
(3) Tathata is the state of general law that covers all the confitioned and the unconditioned which are the natural laws and the Buddhist high principles for leading the people to attain Enlightenment. It is directly related to humanity, society, politics, governments, economics and cultures for the security of the nation and the people's happiness.
Therefore, one who can realize the Tathata, can have mental purity, wisdom, lovingkindness, compassion, and patience; and can support human being and society in general. this is true to the Buddha's words as follows :- "walk, monks, on tour the blessing of the many folks. For the happiness of the many folks out of compassion for the world, for the welfare, the blessing, and the happiness of deities and men."