# §2. Surface syntax decision > Sema language specification — §2 Surface syntax decision. > Generated from `docs/LANGUAGE.md` §2. This is the normative specification; for a guided tour see the Language and Neurosymbolic sections. **Decision: Python-style indentation syntax (`:` + indent blocks), `def`/decorators/ keyword arguments retained — `struct` + `enum` + traits (§3.9) replace `class`; explicitly not a superset; PEG grammar with soft keywords; edition field in the manifest from v0.1.** Rationale ([12 §1–2](./research/12-syntax-dx.md)): - The founder base and the ML ecosystem are Python-first; adoption empirics say familiarity, interop, and existing code dominate intrinsic features ([Meyerovich & Rabkin, OOPSLA 2013](https://dl.acm.org/doi/10.1145/2509136.2509515)). - Code LLMs transfer best to languages syntactically close to a high-resource anchor ([MultiPL-T](https://arxiv.org/abs/2308.09895)); a Pythonic Sema maximizes zero-shot prior transfer and makes the Python→Sema synthetic-corpus pipeline nearly mechanical. - Mojo proved the superset promise is a trap and "Pythonic + interop" is the stable landing ([Mojo FAQ](https://mojolang.org/docs/faq/)); Codon's documented list of dynamic features that break static compilation (monkey-patching, metaclasses, heterogeneous collections, dynamic member addition — [Codon](https://github.com/exaloop/codon)) is adopted as Sema's published "differences from Python" divergence spec. - New constructs are `def`-modifiers (`simulate def`, like `async def`) or soft keywords under a PEG grammar (CPython [PEP 617](https://peps.python.org/pep-0617/)/ [PEP 622](https://peps.python.org/pep-0622/) precedent), so post-1.0 keywords never break identifiers; a Rust-style edition mechanism ([Edition Guide](https://doc.rust-lang.org/edition-guide/editions/)) handles hard promotions. **Rejected alternatives:** braces family (Rust/Go surface) — abandons the audience and the LLM prior for tooling benefits tree-sitter already neutralizes; Python superset — Codon/Mojo demonstrate the compatibility tax and credibility burn; new exotic syntax — zero evidence any intrinsic-syntax bet has ever driven adoption ([12 §7](./research/12-syntax-dx.md)). Keyword disposition versus the brief (evidence-driven changes flagged; details in §5 and the Decision record): | Brief keyword | Disposition | |---|---| | `semantics` | **kept** (expression predicate + block guard) | | `simulate` | **kept** (`simulate def` modifier) | | `testable` | **changed: verification is default-on**; `assure`/`@no_verify` replace the opt-in keyword | | `policy` | **kept** (declaration + attachment) | | `monitor` | **kept** (declaration form), collision risk documented | | `native` | **split**: `native` = bind (C ABI/FFI), `ported` = toolchain-deterministic translation | | self-healing | **scoped, not global**: `supervise`/`heal` blocks; repair-only, "extend/grow" scoped out (D14); phase sequencing per ROADMAP | ---