It’s surprising how many grant applications do not clearly spell out a critical need. A critical need is the fundamental reason why a grant should exist. Without it, there’s really not much of a point to the grant. And yet, a critical need is frequently not stated. The common mistake that people make is that they confuse a gap in knowledge with a critical need. They clearly spell out what gap in knowledge they plan to address. And mind you, that’s an important component of a grant proposal. But if you stop there, if you never explain why there is a critical need to bridge the gap in knowledge, then your application is going to fall short. Unless the reviewers really like you for other reasons, they will probably not be impressed with your grant application.
Let me explain the difference between a gap in knowledge and a critical need by way of an example. Assume you go out Saturday night and get drunk. In the morning, you wake up and have no recollection of how you made your way home. This is clearly a gap in knowledge. But there’s no critical need attached to that gap. I couldn’t care less whether you stumbled home, took a cab, or hitched a ride with a friend. Your grant on “The modes of transportation by which I found my way home last Saturday” is not going to be selected for funding by my agency. Now, instead, consider the following scenario. You go out Saturday night and get drunk. You wake up Sunday morning, not remembering how you got home. Upon looking into the mirror, you find that you’re battered and bruised. You’re also covered in blood. And your husband is nowhere to be found and doesn’t answer his cell phone. In this scenario, I think most people would think that there is a critical need to figure out what happened, to fill the gap in knowledge. Your grant on “Why I am innocent and didn’t kill my husband. Honestly!” would probably fare much better than the previous one.
My point is: there are all sorts of gaps in knowledge that aren’t attached to a critical need. Grants to fill those knowledge gaps will generally not fare that well in review. Therefore, think carefully about the critical need your research will fill. If you can’t think of one right now, think harder. I’m sure you can immediately name the gap of knowledge you’re working on. The critical need should be just as obvious to you. Note: If you’re a junior scientist working on questions that your adviser has funding for, then your work almost certainly satisfies some critical need. If you’re not sure what it is, ask your adviser.
Where in a grant application should you express the critical need? It has to come early, so your reviewers don’t waste a lot of time being bored or disinterested. Also, it needs to be in a position of stress, so your reviewers correctly perceive its importance. Consequently, there’s only a single place in a grant proposal where it fits: the last sentence of the first paragraph. The entire first paragraph should build up to the critical need, which justifies why you’re writing your grant in the first place.
Let me illustrate this idea with the first paragraph of a grant I recently wrote :
Comparative sequence analysis is a cornerstone of modern biology, with applications ranging from determining the evolutionary history of species, to tracking pathogens, to identifying sites in a protein under positive or purifying selection. For protein-coding genes, comparative analysis has shown that protein structure strongly influences sequence variability: buried sites tend to be more conserved, and exposed sites—more variable. Deviations from this expectation can suggest functional importance. For example, a rapidly evolving buried site in a viral enzyme might be near the binding pocket and contribute to the evolution of drug resistance. A conserved exposed site might be involved in important protein--protein interactions. Yet conventional tools for comparative sequence analysis ignore protein structure and operate on sequence data alone. We, therefore, see a critical need to develop comparative methods that can jointly analyze sequence and structural data.
This was the first paragraph of the Aims page, arguably the first piece of text in the grant that the reviewers read. As you can see, the entire paragraph builds up to the critical need, which is to develop comparative methods that can jointly analyze sequence and structural data. This is a critical need only because we believe—and have some preliminary data to demonstrate—that sequence analysis in a structural context will be more informative for important applications than sequence analysis in the absence of structural information can be. If there weren’t any important applications, or if the structural information made little difference to the outcome of the analysis, then the critical need would evaporate. There’d still be a gap in knowledge around sequence analysis in a structural context, but there wouldn’t be a critical need to bridge that gap.
 For full disclosure, I should say that this grant wasn’t funded. However, it was scored in the top third of applications (26% percentile). From my reading of the reviews, I would say that the reviewers believed our critical need. We just weren't sufficiently competitive with the actual work we were proposing. Specifically, we didn't have sufficient preliminary results to give our proposal that aura of magic.