Telling knitting from crochet

It came as a surprise three years ago when I started crocheting to hear people call it "knitting".  Nobody who crochets or knits confuses the two, and most people who do a few textile arts can tell the difference at a glance.  But a large number of people who don't do either craft haven't any idea how to distinguish them.  

The sofa blanket and pillow above are both crochet.  If you want to get fancy, the blanket is filet crochet. Filet crochet is a technique that uses two stitches of different sizes to create patterns, using the negative space generated by the smaller stitch for contrast.

If you see someone making fabric and are trying to tell whether it's crochet or knitting, the absolute giveaway for crochet is a hooked tool.  If you aren't standing quite close enough to see whether there's a hook on the end, count the implements.  One short tool is always crochet.

Crochet also holds very few stitches.  If you see only one loop of yarn on the tool (or just a couple), you're looking at crochet.

Knitting uses at least two sharp ended needles with dozens of stitches all looped around the needles at the same time.

Knitting can be reproduced by machine, but crochet has to be made by hand.  So everyone owns a lot of knitted items.  T-shirts, socks, sweatpants, and mass produced sweaters are all knitted items.  Crochet has its own distinct stitch patterns that won't look like anything in your sock drawer.

Knitting is good at creating soft stretchy fabric such as socks.  Crochet tends to be stiffer so it's good for sturdy items such as placemats or tote bags.  It's easier to make fancy patterns with crochet and crochet produces fabric somewhat faster than hand knitting.

Crochet is inherently denser than knitting and uses one-third more yarn to produce the same sized item.  That sofa blanket in the photograph weighs about ten pounds.
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Image credits:
http://en.wikipedia.org/wiki/File:Pink_knitting_in_front_of_pink_sweatshirt.JPG
http://en.wikipedia.org/wiki/File:Crochet-round.jpg