続(つづ)けるTo continue

なおす can be attached to the stem of other verbs to express the idea of 're-doing' or doing something over. つづける can be attached to verb stems in the same way, but expresses the meaning of 'continuing' to do something. For example, やりなおす means 'to do over', while やりつづける means 'to keep doing'.

ている expresses an ongoing action or state. つづける attached to the verb stem expresses a similar meaning, but with a greater emphasis on the idea of continuation. For example, 増えている means that something is increasing or has increased, while 増えつづけている carries the additional nuance that it is continuing to increase.

Both つづける and てくる can show the progression of an action over time. つづける attaches to the verb stem and focuses on the continuation of the action itself. てくる uses the て-form and emphasizes that the action started in the past and has continued up to the present.

つづける and ばかりだ both show continuation, but with different nuances. つづける attaches to verb stems and shows simple ongoing action, e.g. 減り続けている 'is continuing to decrease'. ばかりだ adds the sense of 'more and more,' often negatively, e.g. 減るばかりだ 'keeps on decreasing'.

つづける and 一方だ both indicate continuation but differ in tone. つづける means a simple ongoing action, e.g. 減り続けている 'is still decreasing'. 一方だ follows dictionary-form verbs and adds a sense of progression in one direction, often negatively, e.g., 減る一方だ 'is getting worse and worse'.

ている is a common structure in Japanese to express an ongoing action or state. つづける attached to the verb stem expresses a similar meaning, but with a greater emphasis on the idea of continuation. For example, 増えている means that something is increasing or has increased, while 増えつづけている carries the additional nuance that it is continuing to increase.