The three ways
The trident is a symbol of Poseidon's power over waters. Firstly, it is a symbol of the thunderbolt. Its spikes are flashes, result of the interactions between clouds carrying rain.
The flashing light symbolizes the illumination that, suddenly, lights up the obscure depths of our being. The propagation and the amplification of the generated vibrations let us discover the being's reality, the totality of his states associated with the “Invariable Path”.
The clouds are assimilated to the celestial, essential or “Upper Waters” related to the informal world, the non manifested and supra-individual states. The “Upper Waters” are apparently opposed to (and complementing in reality) the terrestrial, substantial or “Lower Waters”, which are part of the formal world, the manifested and individual states.
The rain corresponds to a descending movement from Heaven to Earth, from informal towards formal manifestation, which conveys a metaphysical world vision. This movement goes with an ascending movement from Earth to Heaven, from formal towards informal qualified as “Waters rising towards Heaven” and reflecting a cosmological world vision. Following the descending or ascending way implies for the being to die in certain states and be re-born into others according to the deadly and invigorating, destructive and re-generative lightning.
These two ways, depicted by the lateral trident spikes, are incorporated into the central spike symbolizing the “Middle Path”. It is about the direct way, the most difficult one that allows going, without beating around the bush, from the formal to the informal manifestation, from the terrestrial or individual to the celestial or supra-individual world. It corresponds to the return to the “primeval” state and Waters. The trident is a symbol of Poseidon's power over the sea, which he can rouse (“Lower Waters”) or send back to slack (“Primeval Waters”).
In the Buddhist tradition, the trident is considered as the Triple Jewel symbol. For more details on this subject, see the Tibetan flag.
The triple time
The trident middle spike, sharpened on both sides, reminds us of the Roman double face God, Janus. Looking to the front and the back simultaneously, he brings together, in one being only, the past and the future. However, between the past which is not there anymore and the future which is not here yet, stands the true face of Janus, the invisible face of the present.
The present of the temporal or formal manifestation is only an elusive instant, but when the being rises towards the informal world, he sees beyond the time, he sees everything in the perfect simultaneity of the eternal present. Janus is not only the Master of the “triple time”, he is first and foremost the “Lord of eternity”.
The third face of Janus is comparable to the third frontal eye of Shiva. Placed between the moon and left eye related to the past, the sun and right eye associated with the future, the third eye symbolizes the eternal present. In contrast to certain representations, it is a perfect symmetrical drawing alongside the example of the trident middle spike. Moreover, Shiva has the vajra as attribute, a weapon with a triple spike at each end. For more details on this point, see the vajra
Overall and beyond the ascending and descending ways between Heaven and Earth, the trident symbolizes the third way, the “Middle Path”, the way to eternity.