Different design disciplines are characterized by particular gestures that distinguish them from other design disciplines. For example, the core of graphic design is a visual gesture. This could be something rudimentary such as marks made on a wall with a piece of charcoal, or a more complex expression such as a computer-rendered artifact mechanically reproduced at scale. Whatever the case, absent a (relatively) permanent visual expression you don’t get graphic design at all; you’re dealing with a different discipline.
Different design disciplines also aspire to particular outcomes. A graphic designer wants her posters to be engaging and memorable; an architect wants his buildings to be useful and to fit with their contexts; information architects want information to be findable and understandable. In all these cases, this is achieved by establishing particular configurations of things — visual marks, forms and spaces, labels in a navigation system — that make this work different from any other.
This calls for making choices. The possibilities open to a graphic designer or an information architect are almost limitless. Designing is in some ways about narrowing down the options: selecting (from among the myriad possibilities) a set of relevant items and establishing (from among the myriad possibilities) particular relationships between these items. In other words, design is a process for establishing order in a small part of the universe, towards desired outcomes.
Consciously or not, designers bring to the process rules and techniques that help them make decisions about what to leave out and what to include. Some of these rules are dictated by physiological constraints (e.g., door openings must have a particular width if they are to allow most humans to pass), some are part of the canon for the discipline (e.g., some configurations of spaces have emerged over time as being more practical than others), others represent cultural assumptions that inform the designer’s worldview (e.g., what constitutes a traditional house varies around the world), and still others may reflect popular tastes that change over time.
These rules and techniques represent possible responses to design problems. You can think of them as the toolset that designers bring to the shepherding of chaos towards useful order. If all you have in your toolset is a hammer, all problems look like nails — and you’ll have a hell of a time (and possibly do lots of damage) trying to hammer a screw into place. It behooves you to avail yourself of — and learn to use — a screwdriver. A designer with a wide variety of possible responses will be more effective than one with a smaller set.
In this sense, design is the opposite of ideology. Ideology is an attempt to reduce chaos — to narrow choices — through a predefined, abstract, rigid view of how to best achieve particular outcomes. Design, on the other hand, is about reducing chaos through an emergent, responsive, tangible view of how to achieve particular outcomes; a feedback loop that takes real-world conditions as its baseline. To effectively lead this process, designers are called to be open-minded; to learn from everything and everyone without ideological entanglements; to expand their variety of responses as much as possible.