Facts

Parties and proceedings: The appellant ([A.] ), widow of [G.] , who died in June 2007, is an heir together with her five stepchildren (respondents). The estate included several agricultural plots leased out, which were recorded in the inventory of the [T.] Notariat at their earnings value.

Estate partition agreement: On 29 September 2007 the parties concluded an estate partition agreement under which the appellant received CHF 310,000.-- from the marital property according to the inventory taken on 25 July 2007; her inheritance share was thereby settled in full in respect of all claims.

Consequences: The compensation fund rejected the appellant's application for supplementary benefits; the reasoning was that she had waived claims of at least CHF 236,480.-- through the inheritance settlement.

Action: On 27 March 2016 the appellant challenged the estate partition agreement. Following the conciliation certificate of 11 July 2017 and the action of 10 November 2017, she primarily sought annulment on the ground of error (prayer for relief no. 1), payment of CHF 1,224,081.75 less CHF 310,000.-- (no. 2), registration as joint owner of five plots (no. 3), and, in the alternative, payment of CHF 716,500.-- based on a right to a share of profits (no. 4). The District Court of Frauenfeld dismissed the action.

Lower court: The Cantonal Court of Thurgau (judgment of 19 December 2019, ZBR.2019.32) upheld the appeal on the alternative point (profit-sharing right) and remitted the matter to the District Court; it dismissed the main claim (error). It found no mistake as to the basis of the contract, because the appellant had made no enquiries, it was not recognisable to the respondents that market value was meant to be the basis of the contract, and the appellant had conducted herself as if she wished to withdraw from the estate as quickly as possible.

Before the Federal Supreme Court: The appellant requests annulment and reversal of the estate partition agreement, payment of CHF 914,081.75 plus 5% interest since 11 July 2017, and the land register entries; in the alternative, remittal. She also requests legal aid. The respondents request dismissal of the appeal.

Central question: Whether the appellant can successfully rely on a mistake as to the basis of the contract (Art. 24 para. 1 no. 4 CO) because, under the correct legal position, the plots should have been credited at market value rather than earnings value.

Considerations

Admissibility (consid. 1): The appeal is directed against a remittal decision, which in principle is an interlocutory decision. However, the Federal Supreme Court classifies the dismissal of the main claim as an appealable partial decision under Art. 91 lit. a FSCA, since in the case of main and alternative claims (objective joinder of claims) the main claim can be assessed independently and the dismissal becomes final. The amount in dispute, standing to appeal and time limit are complied with.

Standard of review (consid. 2): The Federal Supreme Court applies the law of its own motion but is bound by the facts as established by the lower court (Art. 105 para. 1 FSCA). A complaint regarding the facts requires arbitrariness (Art. 97 para. 1 FSCA; Art. 9 Cst.), and the strict principle of complaint (Art. 106 para. 2 FSCA) applies.

Mistake as to the basis of the contract (consid. 4.1): A mistake as to the basis of the contract under Art. 24 para. 1 no. 4 CO exists where a person was mistaken about a circumstance which was a necessary basis of the contract for that person and which, in good faith in commercial dealings, that person was entitled to regard as a necessary basis. Subjective and objective materiality are both required. Negligence does not in principle preclude reliance on error but leads to liability for damages under Art. 26 CO. However, good faith (Art. 25 para. 1 CO) sets a limit: if a party disregards a question that obviously arises, the other party may infer that the circumstance is not regarded as a necessary basis, and reliance on error is excluded.

Question of fact and findings (consid. 4.2): Whether an error existed is a question of fact. It is binding that the appellant mistakenly proceeded from the earnings value, although the plots no longer constituted an agricultural business within the meaning of the RLRA (Art. 7, Art. 8 lit. a RLRA), and that the respondents too had not recognised market value as decisive. New factual submissions by the respondents in their reply (family discount, intention to benefit, quick withdrawal) are disregarded under Art. 99 para. 1 FSCA.

Deliberately maintained ignorance (consid. 4.3): The lower court had denied the error because the appellant had failed to make enquiries. The Federal Supreme Court notes that a person who knows of their own ignorance is not mistaken (deliberately maintained ignorance, speculation rather than error). However, this is a question of fact and requires findings as to knowledge and intent at the conclusion of the contract. The lower court made no such findings; deliberate ignorance can therefore not be assumed. Negligent failure to make enquiries does not exclude error. The objection of a breach of good faith also fails, since the respondents themselves were under the same mistake and no expectations arose that could be disappointed.

Mistake of law and materiality (consid. 4.4): The error concerns not merely an immaterial legal consequence (loss of supplementary benefits),…