Could this be done without our knowledge? Could advertisers use subliminal messages, against which the masses are but powerless followers?
What about a political campaign? Could they implant a subtle idea which we might react to? Yes of course, they try it all the time; it’s called "advertising". A perusal of the internet will land you with many examples where this will be the case.
There is some confusion though. James Vicary's "Coca Cola" experiment attempted to prove subliminal advertising works, but cooked the statistics and later had to recant. It had created such a stir that the US Congress had already enacted legislation to ban their use. Many were left thinking that this meant that there was subliminal messaging didn't exist. But they were stone cold wrong. Since then research has proven they are real and are extremely powerful. You'll find most of the work in the US National Library of Medicine.
When you are exposed to advertising, you are rather complicit in the influence - you realise you're looking at an advert where you know it's the job of the advert to influence you. You are also aware that you didn't choose the message or the message, whatever it is may be out of alignment with what believe.
This is where most self-development programmes which use subliminal messaging fall down. You may want to choose A over B – but without your conscious effort to reinforce this behaviour or decision from within you, your results are minimal.
Rather, subliminal messaging works by installing the components of a formulated idea into your subconscious, but it cannot manifest this idea without the help of your conscious mind; your conscious effort, awareness and intent. They can prepare you to act or feel, but does not cause or drive the real change. It is only when the conscious mind works toward congruence both emotionally and intellectually with the deeper self that true and dramatic change happens.
This means advertisers can't do anything little more than raise your awareness, make buying their brand feel good (for no real reason sometimes), and keep their brand within your consideration set - they cannot force you subliminally to buy. But this means that sadly that one cannot outsource often difficult journeys of self-development. There is no magical switch. No matter how self-improvement experts might market themselves - you know it's not true. There are no words which can magically control you. Only you can decide.
Deep down you know this to be true.
Advertisers know this too.
Subliminal influence is a pretty nuanced idea to grasp. Think of your dreams. They are nothing more or less than your subconscious thoughts left to go haywire while your conscious mind rests. Your dreams can sometimes enlighten and influence you; they do not control you.