Another key concept: "mode" or modum. He uses the same verb intelligo
which translates as "I mean" or "I understand." The translation "I
mean" might be more accurate. "Modifications" seems to be an excellent
rendering of affectiones, retaining the root of the word modum itself. "Affections" seems to be heavy
with connotations that I doubt Spinoza holds here and, further, are misleading enough to create significant confusion in later books on emotions. Next, I also think
that translations of "substance" should not be modified (no pun
intended) by an indefinite pronoun (as in "a substance"), as it would
appear from an earlier observation that substance is logically not
plural.
This first part seems clear enough with his clarification following sive or "or." He describes "mode" as id quod in alio est or "that which is in another." This is as opposed to I.D3 where Spinoza describes "substance" as id quod in se est
or "that which is in itself." His clarification on the meaning of this
term is explained in I.D3: "is conceived through itself" as meaning
"that whose concept does not require the concept of another thing, from
which it must be formed." Thus, his meaning in I.D5 must follow when he
states "through which it is conceived" to be roughly "that whose concept
does require the concept of another thing, from which it must be
formed." Clearly a "mode" does not qualify as causam sui or "self-caused" of I.D1.
A remarkable issue lies in the middle of the definition. Spinoza is not always careful with his writing - particularly in the scholia. However, it would be unlikely that these first definitions were not carefully written and subsequently scrutinized. Every word is too important. Thus, the use of the plural affectiones or "modifications" to match with the singular modum or "mode" is remarkable - when the rest of the definition returns to the singular. Most translators treat it as simply a kind of categorical plural which then simply goes back to the singular after sive. Other translators convert it to a singular as a "state." But, I think both approaches are mistaken. Instead, I think that modum is a complex item which is made up of multiple modifications, which as an entity that might be in some sense considered a whole is then able to be "in another" or "conceived through another." he plural signifies the lack of such a thing as a truly simple body. Later in the work, he hypothesizes the existence of a simple body for discussions of motion and rest and then dismisses such existence after he has established the principles involving motion and rest require complex bodies made up of complex parts.
Spinoza again raises the mind-body issue as in prior definitions because he discusses not only the “body” aspect with a mode being in another, but also the “mind” aspect by the mode being in another through which it is conceived. This mind-body aspect is similar to I.D1 – I.D3 because it uses the verb “conceive” rather than the verb “perceive.” This means that the mode, even with its limited function, is discussed in a “view from nowhere,” that is the realm of Being and Knowing.
Per modum intelligo substantiae affectiones sive id quod in alio est, per quod concipitur.
Translated as,
By mode I understand a modifications of substance, or that which is in another through which it is conceived.
