I have written posts on the Ajapa mantras, Soham and Hamsa earlier (index). Soham and Hamsa are the same energy, they both will take you to the same destination, they are both equal. But there is a subtle difference in the thought that they express, both routes are slightly different. 

The Ajapa mantra are inherent in the sounds embedded in the breath. All living beings continuously recite the Ajapa mantra with every breath they take, but unconsciously. The initial objective of spiritual practice is to become aware of this continuous mantra jaap. This 5 layered body, panchakosh in which we, the individual soul, exist in, is ‘made from’ this Ajapa jaap, the ‘soundless speech’.

The sound ‘Sa’ exists in the inhalation/ Purak and the sound ‘Ha’ is embedded in the exhalation/ Rechak. And as I have mentioned earlier also, when you reach the Unmani avastha, the Ha and Sa vanish, ie you stop exhaling/ inhaling and remain in the Kumbhak state, this is the 4^th stage of Om. The goal of spiritual practice is to go beyond the sound form of Consciousness, Shabda Brahma and reach into the soundless Arth, the Self hidden in the sound. Thus the Ajapa mantra are a fast track system for Moksh.

Om has four stages (ref Mandukya Upanishad). Waking – Jagrut, dreaming – Swapna and deep sleep – Sushupti are the three routine stages which we all go through in our lives. The silence that comes after you recite the Om is the fourth stage. In this state, the Mind is in the Unmani avastha and you are in your Self. When this stage occurs during Dhyan, it is called ‘Samadhi’, or more properly it is the Turiya state of the Vedant. You cross the boundaries of the creation and exist firmly in the ‘Soundless’ Atma. For the spiritual aspirant, this stage occurs temporarily while sitting on the Asan. The objective of all spiritual practice is to exist in this stage always, this is called the Parama-hamsa or the Jivanmukt state. 

This subtle analysis of Soham and Hamsa is just a technicality. You can approach the Atma, the Self, from either direction. Both are the same energy and have the same power to pull you towards yourself. 

Soham – When you start your Dhyan with an inhalation and end it in an exhalation the mantra is ‘Soham’ ‘Sah Aham’ सः अहं, I am He’. Here the idea expressed is ‘Aham Brahmasmi’. I am that Atma. You can understand Soham in two ways depending on your level of evolution.

• If you think that you are the Jivatma, then the subject ‘I’ is creation/ Maya/ Shakti or the jivatma the individual soul. With every ‘Soham’, the Jivatma says that it is the Atma/ Advaita / the ultimate auspiciousness, ie the Para Shivah itself. By continually asserting this fact, with time, transcendence takes place. In one line, ‘When Shakti looks at Shivah, it says Soham’ 
• If you are confident that you are the Atma, the Advaita. Then Soham also means that the Para Shivah is continually reasserting that it is verily the Self. This is the Anuttarah avastha or the Vedant Vichar, also called the Turiyateet in some books. In one line, ‘When Shivah is in itself, it is Soham’.

Hamsa – if you start your Dhyan with an exhalation and end it with the inhalation then the Ajapa mantra is ‘Hamsa’ ‘He is Me’. Here the idea expressed is more on the lines of ‘Ayam Atma Brahma’. If you analyse the Mahavakya, then the fourth one in sequence is that ‘everything around me is verily my own self’. This is the expansion of the identity to encompass everything and everyone.

• So in this thought process, with every ‘Hamsa’, the Atma/Brahma is saying that everything or all creation or Maya or Shakti is the same Me/ Atma/ Brahma. With Hamsa, the Ultimate Shivah says that he himself is the manifested Maya. In one line, ‘when Shivah looks at Shakti, it says Hamsa.’ 
• Also ‘When Shivah is in itself, it is Hamsa’. The Advaita Shivah is continually asserting that ‘it itself is the only known’.

But still, for beginners on the spiritual path, I would recommend ‘Soham’ as the easier path. Right now, we are all under the impression that we are the Jivatma thus ‘Soham’ vichar/ thought is more suited for this mindset. Soham is the samhaarrupa of the Paramatma, ie it will destroy the anandmayikosh, ie linga sharir which is the seat of ignorance. It will also destroy the sachit karma and change the perception from the limited jivatma to that of the Advaita Paramatma.

The foundational thought/ Vichar of the Vedant is Soham as Aham Brahmasmi and also the Hamsa as Ayam Atma Brahma. And these two, Soham and Hamsa are also used in several mantra, yantra and tantra. You will find references to Soham and Hamsa in several standard books in the Upanishads and also in the Tantra.

Both are equally powerful and whatever you practice, keep on doing it. Convert every breath consciously into the Ajapa Mantra and be the Self.

(This mini-post is in response to a question on Hamsa and Soham)