The difference between a pergola and an arbor is quite subtle in most cases, and many people consider a pergola and an arbor to be essentially the same thing. An arbor is generally much smaller than a pergola, however, as a pergola often covers an entire walkway or living space, while an arbor only covers a small space and acts as an entrance or gateway to a particular area. Both can be made in a similar style and may look almost identical, but the pergola will be much longer and often wider than an arbor.
Another difference between a pergola and an arbor is seating arrangement: an arbor often features a bench on which visitors can rest and find protection from inclement weather, while a pergola can cover an entire area designed for seating, a table, or other types of arrangements. Pergolas sometimes cover patio areas and offer shade from sunlight, and chairs and tables can be set up on the patio underneath the pergola to form a comfortable and attractive shelter. An arbor is much smaller and only allows only one or two people to sit beneath it at one time, as it is meant as a temporary shelter only.
Part of the reason why a pergola and an arbor often get confused with each other are the design similarities: a common pergola design features posts that support horizontal beams, and across those parallel horizontal beams decorative wooden slats are secured at intervals. This allows some sunlight to pass through while still providing shade when the sun is at an angle. An arbor may share this same design but on a much smaller scale, causing some people to confuse the two structures. Some arbors feature trellises on either side to allow plants to climb up and over the structure. Pergolas may feature trellises as well, but most pergolas are too large to be completely lined with trellises.
Another way to distinguish between a pergola and an arbor is the construction of each structure. A pergola can be made as a freestanding structure, but sometimes the pergola is attached to a home or other larger structure. Since many patios are adjacent to homes, pergolas are built attached to the home to accommodate the patio area. Arbors are rarely, if ever, attached to a home or other structure, as the arbor is supposed to be free-standing to indicate an entryway to a specific area.