It is difficult to understand the exact limits of perishus (restraint) by looking at the relevent chapters of Mesilas Yesharim. (In all of the following, I am using quotes from the on-line copy of the translation by R’ Aryeh Kaplan.) In the third sentence or so of chapter 13
The rationale of Separation is epitomized in the words of our Sages of blessed memory (Yevamoth 20a), “Sanctify yourself through what is permitted to you.” This is the signification of the word “separation” itself i.e. separating and withdrawing oneself from something, forbidding to oneself something which is permitted. The intent is to keep oneself from that which is forbidden, the understanding being that a person should withdraw and separate himself from anything which might give rise to something that could bring about evil, even though it does not bring it about at the moment and even though it is not evil in itself.
Perishus is avoiding challenges that one might not successfully pass that which “could bring about evil”. Which explains the Ramchal’s progression in the text that follows the above:
If you look into the matter you will perceive three distinct levels – the forbidden things themselves, their fences (the edicts and safeguards that our Sages of blessed memory made binding on all of Israel), and the “withdrawals” that those committed to Separation must create for themselves by circumscribing themselves and building fences for themselves; that is, by abstaining from things which were permitted, which were not proscribed to all of Israel, and separating themselves from them so as to be far removed from evil.
Perishus is non-binding and non-national, but an extension of the same idea as gezeiros.
Similarly in the next chapter, the Ramchal divides perishus into perishus behana’os, (restraint from pleasures) perishus bedinim (restraint in law) and perishus beminhagim (restraint in conduct, not “minhag” in the sense of tradition. This is described as including hibodedus and shetiqah).
This is perishus bedinim:
It has already been indicated that those who practice Separation may not guide themselves by what is permitted to all of Israel, but must withdraw themselves from what is repulsive, from what is similar to it, and from what is similar to what is similar to it.
So far so good for my theory. The only problem with the above is the MY’s discussion of perishus behana’os:
Separation in relation to pleasures, which we spoke of in the previous chapter, consists in one’s taking from the world only what is essential to him. This type of Separation encompasses anything which provides pleasure to any one of the senses, whether the pleasure be gained through food, cohabitation, clothing, strolls, conversation or similar means, exceptions obtaining only at such times when deriving pleasure through these means is a mitzvah.
Whereas the Ramchal in chapter 13 talks about the permissible being fine as long as is doesn’t lead to sin, in chapter 14 he is saying the permissible is to be avoided unless it leads to mitzvah.
And in 15, the Ramchal explicitly says he is talking about both:
THE BEST WAY for a man to acquire Separation is to regard the inferior quality of the pleasures of this world, both in point of their own insignificance and in point of the great evils to which they are prone to give rise.
Both positions are pretty well documented in other sources. I would suggest that the kasuv hashelishi (a reference to the hermeneutic rule of resolving a contradiction between verses by turning to a third verse to explicate) is the continuation in ch. 15:
For what inclines one’s nature to these pleasures to the extent that he requires so much strength and scheming to separate himself from them is the gullibility of the eyes, their tendency to be deceived by good and pleasing superficial appearances..
I would suggest the Ramchal’s perishus behana’ah involves first two elements:
1- Restraint from those things that one enjoys to the extent that it overwhelms one’s self control, that get addictive. “ad sheyatzrikh kol kach vetachbulos lehafrisho meihem — that which he needs to try so hard and struggle to separate himself from them”.
2- Avoiding that which leads to sin, by leading one’s soul in the wrong way. As per our opening quote.
In both cases, the issue is desire over self-control, and thus, to explanations of the same basic idea.
This is different than perishus behalakhah, which — like a gezeirah — aims at protection of the letter of the law through habit or accident. (The same distinction, when on the level of rabbinic legislation, is that between din derabbanan and gezeirah. See this earlier entry.)
After that, one can seek perishus beminhag, practices of separation, of finding quiet time to take stock of oneself, listen to one’s soul, and spend time alone with one’s Creator.