B1 vs B2: Two Documents, Two Jobs, and One Strategic Writing Order

One of the most persistent misunderstandings I see in ERC proposals is the assumption that B1 and B2 are simply two versions of the same document, one short and one long. They are not. They serve different purposes, are read with different expectations, and require fundamentally different writing strategies.

Failing to respect this distinction is one of the fastest ways to weaken an otherwise strong proposal.

Who reads what (and why this matters)

B1 is designed primarily for non-specialist panel members. These are excellent scientists, but not necessarily experts in your exact subfield. If you doubt this, look up the panel that best fits your research area at the European Research Council and see how many names you immediately recognize as close peers. Usually, not many.

Historically, this distinction was even sharper: specialists read only B2 and did not see B1 at all. Under the current evaluation process, however, specialists now read both B1 and B2. This change has important implications for how the two documents should be written and how they relate to each other.

What B1 is really for

B1 should be treated as a persuasive sales pitch or extended synopsis. Its role is not to explain every technical detail, but to convince a broad scientific audience that the project deserves to be funded.

A strong B1 does five things clearly and efficiently. It establishes a concrete problem or knowledge gap. It explains why this gap matters beyond a narrow subfield. It shows why existing methods or strategies do not adequately address the problem. It demonstrates why you are uniquely positioned to solve it. Finally, it makes clear that the project represents a significant advance rather than an incremental step.

If B1 is successful, a non-specialist reader should finish it thinking that the problem is important, current approaches fall short, and this PI has an ambitious and credible way forward.

What B2 is really for

B2 serves a very different function. It is a research plan, written for specialists who will scrutinize your logic, feasibility, and experimental design.

Here, reviewers expect clear aims, methodological depth, and realism. Preliminary results should be threaded directly into the relevant aims, where they support feasibility and justify key choices. B2 is not the place for redundancy or for restating the narrative of B1 in more detail.

Critically, B2 must explicitly address pitfalls and contingency plans. This section is often underestimated, yet it plays a central role in convincing reviewers that you understand where the project could fail and how you will respond. In ERC proposals, de-risking an ambitious project is not a weakness. It is a signal of scientific maturity.

Why repetition is now a real problem

Because specialists now read both documents, duplication between B1 and B2 is no longer benign. Repeating the same background, rationale, or claims wastes space and can frustrate reviewers. With only five pages for B1 and seven pages for B2, each document must do distinct work.

B1 should persuade.B2 should convince.

When written with this division of labor in mind, the two documents reinforce each other rather than compete for attention.

Why I recommend starting with B2

Despite the natural urge to begin with B1, I usually recommend starting by writing B2. By this stage, you already know why your research is important and you are well versed in the state of the art. What is often less clear is whether the project truly works as an ERC-level research program.

Writing B2 first forces you to define your aims, build a coherent research plan, and explicitly integrate preliminary results where they matter. This process quickly exposes weak points: missing data, feasibility gaps, or aims that rely too heavily on untested assumptions. Starting early, ideally four to six months before the deadline, gives you time to identify which preliminary experiments are essential and, in many cases, to complete them.

Once the scientific core of the project is solid, writing B1 becomes far more straightforward. At that point, B1 is no longer aspirational. It is a distilled, persuasive narrative built on a concrete plan, much like writing the abstract after the paper itself is finished.

Final thought

ERC proposals succeed when form, audience, and strategy are treated as carefully as the science itself. B1 and B2 are not interchangeable, and they should not be written in parallel without a clear plan. When each document is written for its specific reader, and in the right order, the proposal as a whole becomes sharper, more confident, and far more competitive.