Are Fair Isle and argyle both knitted the same way?

No. Fair Isle is stranded colorwork, carrying two yarns across each row, while argyle is intarsia, knitting each diamond from its own bobbin with no carried strands. The backs look completely different: Fair Isle is full of floats, argyle is clean.

Why does Fair Isle use only two colors per row?

Because in stranded knitting every color not in use must be carried along the back of that row, and carrying more than two at once makes the fabric thick, tangled, and hard to tension. Many colors appear overall, but only two travel in any given row.

Where does the argyle pattern come from?

Argyle takes its diamonds and crossing lines from the tartan of Clan Campbell of Argyll in western Scotland, reworked into knitwear and popularized on golf and sportswear in the early twentieth century.

Side by side

Fair Isle vs Argyle

Fair Isle and argyle are the two great knit colorwork patterns, and they are made by different methods. Fair Isle is stranded knitting: two colors are carried along each row and swapped to build horizontal bands of small motifs, with the unused yarn floating across the back. Argyle is intarsia: large diamonds are knitted in separate blocks of color, each from its own bobbin of yarn, with no strands carried behind. One is banded and stranded, the other is blocky and pieced.

Fair Isle

No. 160

stranded colorwork knitting in horizontal bands · first documented 1850s

Argyle

No. 041

knitted intarsia or printed · first documented 1600s

The differences

Aspect	Fair Isle	Argyle
Technique	Stranded knitting; unused colors float across the back of the row.	Intarsia; each color block has its own yarn, no floats behind.
Motif	Horizontal bands of small repeating motifs (roses, OXO, peerie dots).	Large diamonds on the diagonal, crossed by thin diagonal overlines.
Colors per row	Traditionally only two colors travel in any single row.	As many colors as there are diamond blocks in that row.
Back of the work	Covered in carried floats, which adds warmth and thickness.	Clean, with woven-in ends where blocks meet, no floats.
Origin	The island of Fair Isle in Shetland, Scotland.	The Argyll district of western Scotland, from the Campbell tartan.

Which to choose

If the colorwork is in horizontal bands of small motifs, it is Fair Isle; if it is large diamonds with crossing overlines, it is argyle. Both are Scottish, both are knit, but one is stranded in rows and the other pieced in blocks.

Common questions

Are Fair Isle and argyle both knitted the same way?: No. Fair Isle is stranded colorwork, carrying two yarns across each row, while argyle is intarsia, knitting each diamond from its own bobbin with no carried strands. The backs look completely different: Fair Isle is full of floats, argyle is clean.
Why does Fair Isle use only two colors per row?: Because in stranded knitting every color not in use must be carried along the back of that row, and carrying more than two at once makes the fabric thick, tangled, and hard to tension. Many colors appear overall, but only two travel in any given row.
Where does the argyle pattern come from?: Argyle takes its diamonds and crossing lines from the tartan of Clan Campbell of Argyll in western Scotland, reworked into knitwear and popularized on golf and sportswear in the early twentieth century.

Full entry: Fair Isle Full entry: Argyle

Sources & References

1.Fair Isle (technique), Wikipedia
2.Knitted fabric, Wikipedia
3.Argyle (pattern), Wikipedia
4.Argyle knitwear, Wikipedia