|Robert McCay of Pencak Silat Mande Muda|
1. Geographical/Cultural Differences
Silat is found mainly in Indonesia/Malaysia/Brunei while Kali (including Escrima and Arnis) are from the Philippines.
That said, there is some overlap between them as there was plenty of trade between them. Just as Indonesia/Malaysia/Brunei have Muslim roots, those same roots are also found in the Southern Philippines.
Culturally Silat is so ingrained that silat dances are performed at weddings and other special occassions. The ceremonial dress and wearing of the kris are symbols of the warrior caste and considered formal wear, much as a Scottish kilt and dirk.
The sarong is more common to Silat than it is to Kali, although one can still find Sarong in use all across Southeast Asia including the Philippines and India. As from the photo above, in Silat the sarong tends to be worn doubled over rather than full lenth, to allow better mobility. Use of the sarong as a fighting weapon is well-documented in Silat and the techniques easily transfer to other flexible weapons such as belts, towels, chains, ropes, and the like.
The characteristic weapons of silat include the Karambit and the Kris. Both of these are also found in the Philippines, particlarly in muslim-influenced areas, but can be slightly different in design. The silat kris is often found to have a slender blade which is principally meant for stabbing, while in the Philippines the kris can be as long as a barong, and can even have a more rounded tip, being designed as much for slashing or cutting. In Silat, the kris is often coated in poison, so even a minor wound is lethal.
Of course with so many islands across Indonesia/Malaysia/Brunei, silat styles differ greatly, with some being close in appearance to Chinese Kenpo or Sanda, while others are far more exotic. We expect silat to be more circular than Kali, and to attack the low line in greater intensity with sweeps, takedowns, and leg attacks. On the ground, we expect silat to entangle the arms and legs with locks and chokes, with the intent to submit the opponent. Silat elbows are short and quick, looking less like Thai elbows than we see in Kali. The style is fast and fluid, preferring misdirection to hard contact.
To some, the flow of silat is reminiscient of Brazillian Capoeira.
Silat uses jurus, or forms, to teach beginners how to use basic techniques. Very often these include giving the opponent an opening in order to draw in an attack that can be countered. Thus this stances in silat may look vulnerable, but this is deceptive. The silat artists uses these openings as traps. Finishes often include a final position, as a way of showing that the silat practioner is ready for the next attack. Kicking techniques tend to be low line, and can be delivered in groundfighting as well. Silat is generally a close-range style, including many elbows, knees and headbutts as well as backfists, eye gouges, and claw strikes. This can seem very alien to those familiar mainly with western or Japanese fighting arts, and silat often has a big element of surprise. Silat can be especially effective for smaller users, since it is often low to the ground and up close, which helps negate the reach advantages of taller opponents.
I don't purport myself to be a silat expert, and the above is based on what I have studied and observed, with the dislaimer that there is a vast diversity of silat styles, just as there are variations of Kali/Arnis/Escrima in the Philippines.
Silat is a fantastic cultural study, and the techniques can be formidable. Silat is one of the main influences of Kali Majapahit.