Throughout ancient and medieval history, most of the architectural design and construction was carried out by artisans—such as stone masons and carpenters, rising to the role of master builder. Until modern times, there was no clear distinction between architect and engineer. In Europe, the titles architect and engineer were primarily geographical variations that referred to the same person, often used interchangeably Filippo Brunelleschi is revered as one of the most inventive and gifted architects in history. It is suggested that various developments in technology and mathematics allowed the development of the professional 'gentleman' architect, separate from the hands-on craftsman. Paper was not used in Europe for drawing until the 15th century but became increasingly available after 1500. Pencils were used more often for drawing by 1600. The availability of both allowed pre-construction drawings to be made by professionals. Concurrently, the introduction of linear perspective and innovations such as the use of different projections to describe a three-dimensional building in two dimensions, together with an increased understanding of dimensional accuracy, helped building designers communicate their ideas. However, the development was gradual. Until the 18th-century, buildings continued to be designed and set out by craftsmen with the exception of high-status projects. In most developed countries, only those qualified with an appropriate license, certification, or registration with a relevant body (often governmental) may legally practice architecture. Such licensure usually requires a university degree, successful completion of exams, as well as a training period. Representation of oneself as an architect through the use of terms and titles is restricted to licensed individuals by law, although in general, derivatives such as architectural designer are often not legally protected. To practice architecture implies the ability to practice independently of supervision. The term building design professional (or design professional), by contrast, is a much broader term that includes professionals who practice independently under an alternate profession, such as engineering professionals, or those who assist in the practice of architecture under the supervision of a licensed architect such as intern architects. In many places, independent, non-licensed individuals may perform design services outside the professional restrictions, such design houses and other smaller structures. In the architectural profession, technical and environmental knowledge, design and construction management, and an understanding of business are as important as design. However, the design is the driving force throughout the project and beyond. An architect accepts a commission from a client. The commission might involve preparing feasibility reports, building audits, the design of a building or of several buildings, structures, and the spaces among them. The architect participates in developing the requirements the client wants in the building. Throughout the project (planning to occupancy), the architect coordinates a design team. Structural, mechanical, and electrical engineers and other specialists are hired by the client or the architect, who must ensure that the work is coordinated to construct the design. The architect, once hired by a client, is responsible for creating a design concept that both meets the requirements of that client and provides a facility suitable to the required use. The architect must meet with, and question, the client in order to ascertain all the requirements (and nuances) of the planned project. Often the full brief is not entirely clear at the beginning: entailing a degree of risk in the design undertaking. The architect may make early proposals to the client, which may rework the very terms of the brief. The 'program' (or brief) is essential to producing a project that meets all the needs of the owner. This then is a guide for the architect in creating the design concept. Design proposal(s) are generally expected to be both imaginative and pragmatic. Depending on the place, time, finance, culture, and available crafts and technology in which the design takes place, the precise extent and nature of these expectations will vary. Foresight is a prerequisite as designing buildings is a very complex and demanding undertaking. At all times in the design, the architect reports back to the client who may have reservations or recommendations, introducing a further variable into the design. As the design becomes more advanced and detailed, specifications and detail designs are made of all the elements and components of the building.