“Purpose” can be a confusing term. That’s because it can refer to different aspects of a project and it varies based on perspective, too. The purpose of your project is probably the purpose that you are most familiar with. The purpose of your project refers to one or a set of overarching projects goals. (i.e. What do you hope to accomplish with your design?)
The purpose of a communication (e.g. a document, message, speech, video, or poster) is almost always related to project purpose, but they are not the same. Questions related to purpose of communication might be:
- Why are you composing this particular document?
- What do you want the document to accomplish?
- What do you want the message to convey?
- What do you want to happen as a result of this communication? etc.
Author vs. Audience Goals
In addition, different individuals or groups might see purpose in different ways based on their individual perspectives. The author will ask what he or she wants to have happen as the result of a communication, but the audience will ask how this particular information or message will help them to accomplish their own goals, and that will become the purpose for the audience. Unless purpose is clearly determined by the author and clearly communicated to the audience at the beginning of a communication, author and audience goals may be misaligned or confused. Don’t assume that the purpose of a communication is obvious to your audience. This is one of the chief mistakes that leads to ineffective (confusing, unclear) communications.
Evolving Demands for Communication of Purpose
Of course, for some documents purpose is more self-evident than for others. Particularly at the beginning of a project, when relationships between stakeholders are still new and being established, clear, explicit communication of the purposes of both communications and overall projects goals is of high importance. This is because collaborators are still trying to understand each others’ goals, to “get on the same page,” and to agree on a strategy that will work for everyone. At the early stages, relationships are still low-context with regard to the project, and thus, that context or frame of reference needs to be clearly established. Common communications at this stage are project summaries, emails, proposals, best practices reports, requirements, etc.
In general, in on-going stages of projects, there should be some context established, and communications at these stages are often following-through with some agreed-upon strategy. Logically, their purpose is clear. The more high-context familiarity and awareness of purpose the audience has with a communication before it is presented to them, the less explicit explanation of document purpose will be needed to be written into the document itself.
In later stages, changes to process strategy or the initiation of new project goals or development phases will trigger a renewed need to be more explicit about purpose. These changes create a low-context situation once again, and author/audience expectations must be realigned.
In order to effectively identify your purpose as an author (before writing and in the document itself), as well as to communicate clearly to the audience about how document purpose relates to their own goals/purposes, it’s helpful first to classify your purpose type:
- motivating action
- evaluating past action 
Communications in engineering can fall into any (or several) of these categories, based on stages in the design process. For example, a team might write an exploratory email to find out topics that match everyone’s interests and skill levels. A grant proposal might motivate a potential funding organization to support the project financially, and a best practices report might convince stakeholders to adopt/agree upon specific methods. Project summaries and descriptions might be more focused on informing co-collaborators and educating them about project details and specifications. Evaluation might come into play in progress reports, final projects summaries, and also within other documents to add credibility and critical thought in the form research. Effective research should include evaluations of important projects, data, and conclusions drawn in the past.
Finally, as with audience analysis, determination or “construction” of purpose requires a number of context-based critical considerations. Some questions you might ask to help determine the purpose of a communication might be:
- What situation has created the need for the communication?
- What do you need to happen as a result of the communication?
- What preparation has your audience had to help them expect this communication?
- What might your audience’s goals be at this time, and what can they expect to do with this communication?
- What is the relationship between your goals and you audience’s goals/expectations?
- What framing context will be needed to help your audience accomplish their goals in a way that also accomplishes your goals? 
Asking these questions and completing this critical inquiry will help you decide how to communicate your purposes effectively. Review the resources below for more information about creating a strong foundation of purpose in your communications.
- A. D. Reilly, “Clarification Questions That Work,” in Writing and Speaking in the Technology Professions, D. F. Beer, Ed. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2015, pp. 235–237.
- D. A. Winsor, “Engineering Writing/Writing Engineering,” College Composition and Communication, vol. 41, no. 1, pp. 58–70, 1990.
- J. G. Nagle, Handbook for Preparing Engineering Documents: From Concept to Completion. John Wiley & Sons, 1996.
- W. Diehl and L. Mikulecky, “Making written information fit workers’ purposes,” IEEE Transactions on Professional Communication, vol. PC-24, no. 1, pp. 5–9, Mar. 1981.
- R. J. Nelson, “Preparing to Write the Document: A Worksheet for Situational Analysis in the Workplace,” in Writing and Speaking in the Technology Professions, D. F. Beer, Ed. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2015, pp. 7–11.
- J. M. Lannon and L. J. Gurak, Technical Communication, 14 edition. Boston: Pearson, 2016.
- “The American Society of Mechanical Engineers.” [Online]. Available: https://www.asme.org/gsearch.aspx?searchText=document%20purpose&#page=1,category=. [Accessed: 03-Nov-2016].
- R. Fry, “The technical proposal: technical writing with a persuasive purpose,” in Professional Communication Conference, 1989. IPCC ’89. “Communicating to the World.”, International, 1989, pp. 90–95.