筆，係寫嘢、畫嘢嘅架生，由有長條狀、7 - 20 cm 長嘅筆身或筆杆，加埋出會固態或液態顏色嘅筆嘴組成。筆大至以出嘅顏色嘅物料、用途為分類嘅基礎。

歷史
冇人知一支「筆」幾時出現，筆同畫嘢寫字有唔可分割嘅關係，最早畫或寫嘅嘢間接暗示一支筆嘅出現。𠵱家搵倒最早嘅「畫」就係響公元前三萬到二萬年嘅洞穴壁畫，響西班牙山洞 Cueva de las Monedas 裏面嘅壁畫就有 32,000 年嘅歷史，The paintings were drawn with red and yellow ochre, hematite, manganese oxide and charcoal. It is not hard to imagine that the primitive people required tools to applies the color pigments onto the wall. That tools might be the first pen.
The early known written text could be traced back to the Sumerian, that is 6000 B.C.E. The Cuneiform script, the first written language, was "written" on the clay tablet using a "stylus". Those tools our ancessors used cannot considered as what we today think as pen. They are rather the precussor of pen.
In the meantime, the development of pen was parallel yet independent in many culture. China for example, developed a very different writing instrument for their needs. Chinese brush (毛筆) was the answer to writing for need for the Chinese.

第一支筆
The oldest exciting Chinese brush were found on the 春秋戰國時期的古墓 in 1953 on 湖南長沙市左家公山. The basic of the Chinese brush consists of bamboo boby and the rabbit hair tip which absorbs "ink" and release it as it has contact with the written surface.

毛筆
Marked by the perfect Chinese brush in the East and the Feather pen in the West. For thousand years, those technologies evolved little.

Ancient Time
The modern time demarcates the pen truly portable, reliable and usable pen. The creation of ball pen and feel tip marker is the milestone of the development.

Modern Time
http://en.wikipedia.org/wiki/Fountain_pen#History
http://www.classicwoodpens.com/fphistory.htm
http://www.rickconner.net/penspotters/history.html

墨水筆
The first marker was probablythe felt tip marker, created in the 1940's. It was mainly used for labeling and artistic applications. In 1952, Sidney Rosenthal began marketing his "Magic Marker" which consisted of a glass bottle that held ink and a wool felt wick. By 1958, marker use was becoming common, and people used it for lettering, labelling, marking packages, and creating posters.
Highlighters and fine-line markers were first seen in the 1970's. Permanent markers also became available around this time. Superfine-points and dry erase markers gained popularity in the 1990's.
http://inventors.about.com/library/inventors/blpen.htm

唔係筆嘅筆
因為筆通常都係直嘅，所以個【筆】字就有時會用嚟加強「直」嘅意思，例如【筆直】、「西裝筆挺」等。