Pnas Writing

Main-Text Writing & Structure (pnas-writing)

When to trigger

• The manuscript structure is unclear or out of PNAS order.
• Materials and Methods are missing, or someone wants to push them out of the main text.
• The paper is over the length budget.
• You have not chosen a Classification (major + minor) or keywords.
• The Results read like a lab notebook instead of an argument.

PNAS main-text order

A PNAS research article runs, in order:

1. Title — declarative, specific, parseable by a non-specialist.
2. Author list & affiliations.
3. Significance Statement — ≤120 words (pnas-significance); submitted separately but part of the article.
4. Abstract — ~250-word single paragraph (pnas-abstract).
5. Introduction — the gap and why it matters broadly; end on what you found.
6. Results — argument-ordered (below).
7. Discussion — interpretation and broader significance; PNAS also permits a combined "Results and Discussion."
8. Materials and Methods — kept in the main text (see below).
9. Acknowledgments, data availability, references.

Materials and Methods stays in-text (a key PNAS difference)

PNAS keeps a Materials and Methods section in the main text — unlike Cell or Science Reports, which push methods to supplements/endmatter. Provide enough method in the body to evaluate and reproduce the work; longer protocols and extended data go to SI Appendix. Do not strip the main-text Methods to chase a word count — move detail to SI instead.

Length budget

• Research articles have length limits (commonly framed as up to ~6 journal pages, roughly on the order of ~8 figures/tables and a corresponding word/character budget). PNAS counts the whole package — abstract, main text, figures/tables, and references — against the page/character allowance.
• Confirm the current word/character/page caps and the figure-table allowance in PNAS author guidelines before finalizing; treat any number here as a working target, not a rule.
• Over-length material (extended methods, supporting figures/tables, supplementary text) → SI Appendix.

Classification + keywords (required at submission)

PNAS requires a Classification for every research article:

• Major category — exactly one division: Biological Sciences, Physical Sciences, or Social Sciences.
• Minor subject area: one (sometimes a permitted second) subject within that division (e.g., Biological Sciences → Genetics; Physical Sciences → Applied Physical Sciences; Social Sciences → Economic Sciences). Pick from the PNAS list.
• Keywords: a short set (commonly up to ~5) for indexing.

Choose the classification that matches the handling and review community you want, consistent with the venue call in pnas-fit and the editor choice in pnas-track/pnas-submission.

Structure as argument, not chronology

Order the Results by the logic of the claim, not the order experiments were run:

1. Establish the phenomenon (the headline result).
2. Rule out the obvious alternative explanations.
3. Show the mechanism / generality.
4. Demonstrate the broad implication.

Each Results paragraph: claim sentence first, then evidence (figure callout + numbers), then inference.

Cross-references

• Main figures/tables: "Fig. 1", "Table 1".
• Supporting Information: "SI Appendix, Fig. S1 / Table S1"; datasets as "Dataset S1".

Output format

【Order check】 Title / authors / Significance / Abstract / Intro / Results / Discussion / Materials and Methods / refs — gaps?
【Methods location】 in main text? yes (FIX if missing) — extended detail in SI Appendix?
【Length】 package within budget? N vs cap (confirm guidelines)
【Classification】 major (Bio/Phys/Social) + minor subject chosen? + keywords (≤~5)?
【Results order】 argument-ordered, claim-first? yes/no
【Items in main vs SI】 main: [...] / SI Appendix: [...]
【Next】 pnas-figures

Anti-patterns

• Do not delete the main-text Materials and Methods to fit a word count — move detail to SI Appendix.
• Do not omit the Classification or keywords; they are required at submission.
• Do not structure Results chronologically when a logical order is clearer.
• Do not import a Science Report's "Methods-in-supplement" structure — PNAS keeps Methods in-text.
• Do not treat the Significance Statement or abstract as optional sections.