ANSWER - I don't think it is really a case of one or the other, its a blend of both the psychological affect on the caster and the actual tangible benefits each element brings to a working. It is sometimes hard to separate a genuine effect from a belief in a genuine effect and sometimes with magic the two are so interchangeable that it doesn't really matter all that much anyway.
I'll give you an example. Orange oil is traditionally associated with luck. A traditional association gives you a certain confidence (almost like a placebo affect) in the knowledge that it has gained this association through the trial and error of our ancestors. As I work with it myself and get results that reinforces my own belief it strengthens my personal belief that it will work which adds to the effectiveness of my spell work. However, it is important to think beyond the experiences of others and consider specifically why you choose to use something in a working. Would I use orange oil if I didn't like the smell? No. Would I use it if I didn't have a personal intuition that it brings about luck? No. Would I use it again and again if my own personal experiences had negated the traditional correspondence? Certainly not. When I use something I try to think back to how it gained the association in the first place. Oranges, traditionally hard to grow in colder climates, would perhaps have been a real symbol of success for the few to managed to raise an orange tree. Possibly this is how they gained their traditional association with luck.
By thinking through the reasons behind what I do, I strengthen my own belief in the correspondence and therefore the working. I affect my own belief which has a knock on effect of increasing the power of my intent. There is a fine line between knowing that something will work and believing something will work and like I say, I'm not sure that the distinction is really all that important.
In terms of genuine properties of individual spell enhancements, do I believe they have actual tangible properties in themselves that add power to the spell? Well yes, I do. And again this is borne out through my own experiences as a witch. I don't use salt circles because other witches do, I use them because salt has a genuinely protective property and utilising that property taps into the essence of a power that can be used to enhance my own. Certainly I could substitute a visualisation of a barrier rather than an actual physical salt circle and if you are asking would this negate the power of your candle magic then no, it probably wouldn't. But why would you not utilise other strengths and energies in a blend with your own intent in a spell? I'm a big believer in intent being the key element (though many recent discussions on this subject suggest that a lot of witches are moving away from this in their practise) but intent isn't the sole force behind your power. The knowledge of how to use the energies and attributes of different herbs, crystals and oils does play a part in your work and don't forget that that link with the natural world is a big part of what it is to be a witch.
I'd also comment that sometimes a belief can be strengthened by the number of people believing in it. If witches all over the world believe salt to have protection power, the energy of all that belief may well play a part in fusing salt with that power. Kind of a bit like chicken and egg, which came first the property or the belief in the property. It would be an interesting experiment. Sugar has no discernable protective properties (at least not on my path) - it would be interesting to see what would happen if witches all suddenly started using sugar for that purpose. I'd suspect that eventually a belief would be sustained and a correspondence would be formed. And I wouldn't be surprised if beyond the belief, sugar itself actually did take on the property eventually. Like I say, there's a fine line between belief and reality in the craft.
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