Kaladin's mother talks of everything in the world having a spren. However, there is a quote during one of the bridge assaults that challenges the idea of everything having a spren. Before the side bridge assault, Kaladin thinks that the reason that there are no fearspren around Bridge Four is that all the fearspren are around the other crews.
I purpose that both speakers are correct. All things have a cognitive aspect. However, spren, which manifest in the physical realm, are excitations in the cognitive field. Much like electrons are excitations in the electric field, or Higgs Bosons in the Higgs field. This is also the reason why spren of the same type are virtually identical, just like quantum particles.
This excitation is caused by the perception of individuals. It is enabled by the powers of Honor and Cultivation. This is why there is a limit to the amount of spren in an area; there is a limited amount of shardic power.
In the case of Kaladin and Syl, Kaladin's honorable actions increased the "quantum charge" of Syl. Kaladin can draw upon this increased charge for his surgebinding.
To sum up, spren are created/summoned when a strong cognitive aspect excites or taps into a cognitive ideal. The combined powers of Honor and Cultivation then allow the excitation to manifest in the physical realm. The exact ideal, amount of Cultivation, amount of Honor, etc determine the type of spren, similar to how mass, strong and weak nuclear forces, and charge determine the type of quantum particle.
Thoughts?