Hirhur k'dibbur (conclusion)

I meant to finish the sugya of hirhur k'dibbur started earlier. The Sha'agas Arye asks: why in hil brachos (1:7) does the Rambam pasken hirhur k'dibbur and allow a bracha to be said b'lev, but the Rambam in hil shabbos paskens that hirhur is not included in the issur of "dabeir davar"? Our goal was to illustrate what lomdus was all about. In a nutshell, the ba'alebatish approach is the contrast the case of brachos with the case of shabbos. I bounced this off my wife who immediately responded that dabeir davar is an issur, while making a bracha is a mitzva. What makes this unusual is if hirhur k'dibbur was assur on shabbos but not sufficient for a bracha then such a chiluk would be easy to understand - we treat hirhur k'dibbur l'chumra by issurim. However, how can you explain the reverse chiluk that it works by brachos and but is permitted by shabbos? I think you are forced into a more conceptual framework from the get-go here. The nature of a bracha is to thank Hashem - thoughts of thanks may be sufficient to accomplish that goal. By shabbos, we prohibit acts of chilul shabbos, so thought alone does not fit a category of issur. We might make the following chakira: if one holds hirhur k'dibbur, is one saying that thought is equal to speech, or is one saying that the particular mitzva (e.g. bracha) does not require speech for fulfillment? One possible distinction might be whether the act of writing is sufficient: if hirhur=speech, one has no clear evidence that the same would apply to writing, but if the mitzva per se does not require speech, then writing should be sufficient (see Shu"t R' Akiva Eiger regarding this issue). Using this chakira we can sharpen the distinction we drew above. With respect to brachos, the Rambam may hold no speech is required, hence hirhur k'dibbur, but with respect to issurei shabbos, there is no aveira act in thought. Moving further down the lomdus spectrum, we might pose a Brisker distinction between speech as an act of the gavra, and speech as an object, a cheftza. R' Yosef Engel has an analysis in his sefer Esvan D'Oraysa whether issurim function as prohibitions on the gavra or on the cheftza. Perhaps one could argue that the Rambam would hold that hirhur is equivalent to a ma'aseh on the part of the gavra, but hirhur is intangible and cannot become a cheftza shel issur. Again, this is not a thorough chaburah on the sugya, just thoughts off the cuff, mainly to try to illustrate what I think lomdus means.